Marine Testing & Parameters

Understanding Marine Testing and Parameters

Temperature:

What is it?
How hot or cold the water is. (I know you guys already knew this one).

Why's it Important?
Without going into too much detail, temperature affects the metabolism of every organism in the tank, which in turn affects their biological systems (respiratory, sexual, etc). But what you, the marine hobbyist needs to know is, if it's too cold, or too hot, things won't live. But there's still a wide area in the middle to shoot for. And different organism will thrive or struggle in different ranges. There is still a lot of debate on what the best temperature(s) are for each organism, so I can't really give solid answers in this article. But, I can suggest ranges. In the meantime, I strongly encourage you to do some research on your critters, and find values that make sense to you based on that research.

What Value should I Aim For?
There are many different ranges various hobbyists stick to, and pretty good reasons for each. A lot depends on what critter(s) you are keeping, and how you want them to react. Anything from mid 70's to low 80's can be withstood, and many have had success at all the temperatures in that range.

What's more important that what temperature you aim for, is how much you sway from that target temperature. The key is keeping your tank's temperature in as tight a range as feasible. Ideally a 24 hour period should not have more than a 2 degree temperature swing. A few occasions slightly outside of this range are not detrimental to the tank, but the goal is to try to stay in that range.

The higher the temperature, the faster every critters metabolism will be. This means it POTENTIALLY could fight off infections faster…but it could also shorten the critters life span.
Ich and other parasites are rumored to thrive more in lower temperatures and tend to fade faster in higher temperatures.

What Do the Values mean?
Pretty straight forward answer, it means the temperature of the tank's water in either Celsius or Farenheight degree's. Your tanks either right where it should be, or it's hotter/colder than it should be. Adjust accordingly.

Note that gradual changes/corrections are recommended. If you notice your tank is 5? cooler than what you want, adding boiling saltwater to instantly bring the tank back up to your target temperature will be even more detrimental to the tank. Just correct your heaters and bring the temperature up over time. If the tank's too hot, adding a baggie filled with a few ice-cubes to the sump is a good way to slowly bring the temp back down. If the problem is constant, consider adding a fan over the sump or getting a chiller.

When Should I Test For It?
It really should be checked constantly. Every time you look at, walk by, or are near the tank, you should glance at the temperature.

There are many different devices to test for temperature. There are thermal stickers you can put on the side of the tank. Floating thermometers that either float in the tank, or can be suction cupped to the side. There are even electronic probes that constantly give an accurate digital temperature reading. Since the temperature doesn't really need to be dead-on any exact value, all of them are pretty sufficient. So I leave the choice of which to use, entirely up to you. The more accurate, the better of course, but there are more important parameters to spend money on in order to get more accurate results.

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Salinity:

What is it?
Simply put, it's a test for how much salt is in the water. More scientifically, it's the concentration of sodium chloride in the water.

Why's it Important?
With salinity (like temperature), while it's important to be in the right range, it's more important to maintain as close to a constant value as possible. Salinity's importance in your system, without going into a lot of scientific detail, is related to osmosis and each critter's ability to regulate ions. I include links later on that go much more in depth on this topic, but for now, all you need to know is that it's best to keep the Salinity in the optimal range for the critters you're trying to keep, and maintain this salinity as best as possible. Keeping the tank outside of that range creates stress on your tank's inhabitants, which as previously stated, leads to illness, infections, or even death.

One common mistake/oversight made early on in this hobby relates to evaporation and it's affect on the tank's salinity. Water evaporates from the system. But that's it. Only the water (pure H20) is evaporating. When this happens, the amount of salt (and other chemicals) in the tank remains the same. Only now the volume of water is smaller, which means their concentrations are higher.

This means, to maintain a stable salinity value, this evaporate water needs to be replaced in the system. This is referred to as topping off. The idea is, if your tank evaporates about a gallon a day, then a gallon of fresh (preferably RO/DI water) needs added to the tank to keep the salinity (as well as other parameters) at the same value.

The more frequent the topping off, the more STABLE the salinity will be. With the example I just gave, if you topped off once a week, you would need to add 7 gallons of freshwater. If you did this all at once, this would more than likely be a huge shock to the system, causing major stress on the inhabitants. Topping off once a day is a common practice and for most critters/system sizes, this is sufficient. However this can still be a little shocking to some of the critters in the tank, and more frequent top-offs may be necessary depending on the types of animals you have in your system. Some people even install top off systems that constantly replace evaporated water throughout the day. This type of topping off is the most ideal, and provides the most stability when it comes to salinity.

What Value should I Aim For?
The salinity in the natural reefs can vary from region to region. But the most common value found is about 35ppt (1.026 sg). Again, there are arguments for higher as well as lower salinities. Most seem to recommend aiming for the same levels as the reefs. If you're wondering why most LFS keep their tanks at much lower salinities, it's mainly cost. Much less salt is required to keep large volumes of water at a lower salinity. As with temperature, more important than which actual value you choose to aim for, is that you keep the salinity as constant as possible. Anything in the range of 1.023-1.027 sg should do just fine for most critters. Again, research the specimens your planning on keeping, and find out what their preferred salinity is, and aim for that.

What Do the Values mean?
The 35 ppt value simply means 35 parts per thousand. If you broke down the water into all it's parts, out of a thousand of those parts, 35 would be salt (sodium chloride). Another way to think of it is simply 3.5%.

The 1.026 sg value is a little trickier. The sg stands for Specific Gravity. Specific gravity is not so much a measure in units, as it is a measure of density as compared against pure water. Pure water has a Specific Gravity (density) of 1.0. SG is a quick way to guestimate the salt content of your water. It is not always the most accurate way, however.

In practice, either value is intended to give you a measure of the concentration of the salt content of the water.

One common mistake made early on, is not taking into consideration the affect temperature has on salinity. Since temperature will make the water expand/contract, as a result, this will affect the density of the saltwater.

When Should I Test For It?
This depends on the automation of your system. But early on, it's probably best to test more frequently. Until you get your top off methods down pat, and get into a top-off habit, it is really best to test daily. After you start having consistent results, testing once a week is sufficient. It is also recommended to test right before and after a water change (as well as testing the make-up water too). Other good times to test are:

Anytime you haven't topped off for a while, for whatever reason. Prior to topping off, you should know what your salinity is at. If it's at an extreme, you need to bring it back into range gradually, as opposed to just dumping several gallons of fresh top off water in. While most critters are better able to deal with a sudden decrease in salinity, than an increase, it's still highly recommended to make any drastic correction, slowly.
If there's been a leak. Similar reasons. Slow leaks could have let you top off day to day, and while Saltwater was leaking out, fresh water was being added in. This can lower the salinity. If it's been a while, you again may need to bring it up gradually by topping off with a little saltwater.
Anytime you dose anything significant. If you're adding calcium / alkalinity additives, you should test your salinity more frequently at first. Until you're more familiar with the affects these additives have on your tank, you should keep an eye on your other levels (like salinity) as well.
Anytime you're adding new additions (fish, inverts, corals). You should test your tank's water as WELL as the water your critter came in. If the difference is significant, you should extend your acclimation time.
There are two common ways to test for salinity. The first is a hydrometer. The concept behind the hydrometer is that they have some item float in a solution, and based on how high it floats, or how deep it partially sinks, you can determine the specific gravity (density) of that solution. Commonly sold hydrometers have a floating arm with pre-marked values on the side. You fill them with saltwater, and based on where the arm comes to rest, you can determine the specific gravity of your water.

The other common device to test for salinity is a refractometer. This device uses a few drops of a solution on a prism, and the tester looks through the prism and based on the way the light is refracted (bends), you can determine the salt content of the water based on preset hash marks in the viewer.

Of the two, the hydrometer is usually the cheaper of the two. However, while there are a few accurate hydrometers out there, in general, a refractometer is much more accurate. They are also usually quicker and easier to use. They can be a little bit more expensive, but refractometers are well worth the extra expense. Often, Hydrometers can be chronically lower in readings, and if you aren't positive that your test values are accurate, taking any action to correct that value can cause serious problems down the line.

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pH:

What is it?
The pH value is a measurement of how acidic or base (opposite of acidic) the solution being tested is. Specifically, this is in comparison to pure water (H20), which is neutral, and has a pH of 7.0 (at ~25? C).

Why's it Important?
This parameter is a little trickier to explain, without getting scientific, but let me try. pH is often misunderstood, but is actually an extremely important parameter in salt water tanks, as it affects a lot of different chemical reactions/factors in the tank, and ultimately every critter in it.

The most obvious affect is just the various critters ability to withstand a certain acidity or baseness. If the water is too acidic, or too base, it can downright burn certain critters. But that's more at the extreme ends of the spectrum. In the middle though, slightly incorrect pH can still have profound affects on the system.

Again, without getting too scientific, the pH of the water affects chemical reactions that can take place in that water. Some of these chemical reactions are necessary in the tank, and some of them can be detrimental. The idea is to get the pH in the right range of the tank that promotes the good chemical reactions, and stops the bad ones. I'll go into more detail about this later, but for now I'll give a brief example of each.

A GOOD chemical reaction that we try to strive for in our tanks is Calcification. This is basically animals in your tank growing skeletons, by pulling calcium out of the water. We want our critters to grow, and if the pH is outside the optimal range, this can either become difficult, or downright impossible.

A BAD chemical reaction that can happen when outside the optimal range is that certain key metals/elements in the tank can become toxic, as they take on different chemical characteristics. Also, if the pH is low enough, DEcalcification can actually occur. Which basically means skeletal mass will start to actually dissolve in the water.

In general, think of pH as the tank's ability to promote or stop various chemical reactions from taking place.

What Value should I Aim For?
While I'm sure you're getting tired of hearing this, it still needs said. It depends on what species of creature you're trying to keep. Each critter has its own specific recommended pH range. So research the critters you're planning on having in the tank, and keep that in mind as you read on.

Generally, anything from 7.9 to 8.4 is tolerable. Yet once again, the more important thing here is consistency. 8.1-8.3 is ideal, but many people have successful reefs that have an average pH of 7.9-8.0 or even lower.

In an established tank, from the time the lights come on until the lights shut off, the pH should rise gradually. Without getting to specific, this is due to photosynthesis. Algae and other photosynthetic organisms in the tank begin processing the light. As part of the photosynthesis process, CO2 (carbon dioxide) is consumed and oxygen is released into the water. This CO2 being consumed (reducing overall CO2 levels) causes the pH to rise.

When the lights go out, the pH will start to drop again, over the course of the night. The ideal range your pH should cover during this period is around '0.2'. So some good goal pH ranges are 8.0-8.2 or ideally 8.1-8.3.

Most beginners tend to see ranges from 7.9-8.1. The most common reason for this is poor circulation around the tank. As previously mentioned, CO2 decreases will cause the pH to rise. For the same reasons, CO2 increases will cause the pH to drop. If there isn't good air circulation around the tank, the very act of you and your family's breathing tends to cause higher than normal CO2 concentrations around the tank. This keeps the pH of the tank constantly lower than you may want. Switching your home air circulation's fan from Auto to On (to constantly circulate the air in the house/apt) will work WONDERS if you have this problem. Also, opening doors and windows frequently (weather permitting) will correct this as well. If you can't get around either of those, running some tubing from outside to your tank (most commonly through the skimmer's air intake) will alleviate this as well.

What Do the Values mean?
As stated, pH is the measurement of how acidic or base a solution is, relative to pure water. pH values greater than 7 mean that the solution is more base than pure water, while pH values lower than 7 mean that it's more acidic than water. The farther away from neutral (ph of 7) the value is, the more acidic or base that solution is.

It is important to note that the pH scale is logarithmic. This means that each whole number difference in pH represents in increase in the acidic/baseness by 10 times as much. (i.e. A solution with a pH of 9.0 is ten times more base than a solution with a pH of 8.0. Conversely, a solution with a pH of 4.0 is ten times more acidic than a solution with a pH of 5.0). Worse yet, that means a pH of 5.0 is 100 times more acidic that a solution with a pH of 7.0!

The main thing to note here is that as the pH gets farther away from your goal, the intensity of the pH increases very quickly. pH that's just a little off (~0.2 units) isn't that big of a deal. But a pH that's off by 1 can mean a MAJOR difference.


The pH of Some Common Solutions
Solution pH
Hydrochloric Acid -1.0
Vinegar ~2.9
Milk 6.5
PURE WATER (H20) 7.0
Seawater 7.7 - 8.3
Bleach 12.5
Lye 13.5

When Should I Test For It?
Most of the time, during normal tank operation, it's not a single test result that's valuable. Instead, what's important is the range of the tank's pH (over the course of the day) that's important.

For the values to really give any insight into your tank's condition, at least two test a day over a period of at least 2 or 3 days is needed. As stated above, pH should increase over the course of the day. So telling someone you tested your pH and it was 8.0 doesn't really tell you much. Was that the pH at the beginning of your photoperiod (the time your lights are on), in the middle of the day, or was it at the end? Without knowing that, and also having other test results you can't really know the range the pH is.

So that said, pH should be tested in the morning, and in the evening right before the lights go off. Once you put critters in the tank, these tests really should be done daily or every other day until you're confident in the consistency of your tank's pH.

Any change in your tank's lighting cycle should prompt another series of pH tests. Changes in ventilation, water chemistry, etc should also prompt pH testing.

pH really is a great indicator of the tank's health. As you'll learn later, when the pH is off, it can be the result of other parameters not being in line, or a symptom of potentially serious system problems.

Consider getting a pH probe that gives a constant readout of the tank's pH. They are much more accurate than test kits, and can save you lots of time doing tests. They also help you figure out much quicker when something's not right with your tank. Knowing your tank's pH values and the normal range your tank's pH covers all the time is very valuable information and will be of considerable help in maintaining good tank health.

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Ammonia:

What is it?
Chemically, it's NH3. Basically, it's the amount of fresh wastes in your system. Wastes like excess food, fish poop, dead critters, etc go through various stages as they break down. Ammonia is a main chemical created during the first stages of waste breakdown.

Why's it Important?
Ammonia is very toxic to most animals that we try and keep (fish, inverts, corals, etc). Ammonia is toxic to pretty much anything but certain bacteria. With fish, for example, ammonia in the water will actually burn the fish's gills and eventually result in death.

That said, Ammonia, in truth, is almost always present in a tank with any life in it. But as I also stated, there are bacteria that consume ammonia. The key here is to get just the right population of those bacteria that can consume the amount of ammonia that's being produced in the tank. If it's consumed at a rate equal to the amount that's being produced, it's not in the water column long enough or in large enough quantities to cause any of the animals any harm. This is part of the Nitrogen Cycle that we all must go through when we first set up our systems. The idea being to allow populations of these ammonia consuming bacteria to reach an equilibrium.

This means the amount of food for each critter roughly equals the amount of critters needed to consume that food. Not just with the critters we bought, but with the other life that forms that will grow in the tank over time (little detritus eating worms, bacteria, crustaceans, snails, etc).

What Value should I Aim For?
Plain and simple, 0 ppt at all times. As I mentioned before, there is constantly ammonia being produced in the tank. However, it should be consumed at a rate equal to how fast it's being produced. As a result, an established tank should have 0 readable ammonia levels.

What Do the Values mean?
Simply put, the test's value will tell you how much detectable ammonia is contained in the water. The values for ammonia are commonly given as ppt which means parts per thousand. This means if you broke down the water into all its parts, for every thousand of those parts, this value is how many of those parts would be ammonia.

When Should I Test For It?
Ammonia should be tested for during the tank's initial cycle or whenever there's been a problem with the tank. During the initial cycling of the tank, ammonia levels (when combined with nitrite levels) can tell you how far into the beginning of the cycle your tank is. Since it is highly suggested that no critters be present in the tank at this point, and ammonia usually only shows up at the beginning of the cycle, the frequency of testing is purely up to your curiosity. Testing daily is good practice, and gives beginners something to do, while helping them get familiar with the testing process, but it is not necessary.

Another important time to test is any time there's been a problem with the tank. Anytime a critter has died, ammonia levels can spike for a bit in the tank. The severity of this ammonia increase is usually relative to the size of the critter (decaying mass). The death of a larger fish can potentially crash a tank, if the body isn't consumed or removed quickly. While smaller fish are usually consumed or breakdown without any noticeable ammonia increase. The death doesn't have to be just Fish, either. The death of a snail, shrimp, or any other critter can also cause an ammonia increase.

Unusually large overfeeding can also cause increased ammonia levels in the tank. Accidentally dropping in half a can of flake food or having your 3-year old child try to help by dropping a whole tray of frozen fish food into the tank are more common than you'd think. Incidents like this can lead to elevated ammonia levels for a while.

Since Ammonia values in a normal, established tank should always be zero (detectable). Other than the above mentioned situations, the decision to test for ammonia is entirely the hobbyist's decision, and rarely needed.

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Nitrites:

What is it?
Simplest way to explain this one is, there are bacteria that process (consume) ammonia. During this process, those bacteria give off/create nitrites. It is (for the purposes of the marine hobbyist), the 2nd stage of waste breakdown. Nitrites are also toxic to most marine life.

Chemically, it's described as N02-

Why's it Important?
Nitrites affect your system in much the same way Ammonia does. It's a different chemical, but the affects are still the same. It's poisonous to the critters in the tank. Nitrites are the by product of the bacteria that are consuming/processing the Ammonia. Again, the goal is to reach equilibrium with nitrites being produced at the rate they are being consumed by bacteria.

What Value should I Aim For?
Same as Ammonia, for all the same reasons. The goal is 0 detectable nitrites. Any more than 0 readable nitrites can be toxic.

What Do the Values mean?
Simply put, the values tell you how much Nitrite is contained in the water. The values for nitrites are commonly given as ppt which means parts per thousand. This means if you broke down the water into all it's parts, for every thousand of those parts, this value is how many of those would be Nitrites.

When Should I Test For It?
Only during the initial cycle of the tank, and possibly anytime there's been an ammonia spike in an established tank. Even then, nitrite levels only satisfy curiosity. Without a series of ammonia, and nitrate test results, nitrite test results alone tell us very little.

Honestly, there is very little practical value to testing for nitrites. Early on, it's good practice for someone just entering the hobby. It also helps them become more familiar with testing procedures as well as letting them watch the nitrogen cycle progress in their new tanks. Other than that, there's no real reason to ever test for Nitrites in an established tank, as its value alone provides no real information.

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Nitrates:

What is it?
Easiest to think of as the 3rd stage of waste breakdown. Again, there are bacteria that process (consume) nitrites. During this process, those bacteria give off/create nitrates. Nitrates at high levels, CAN be toxic to the majority of marine life, however, since it's not nearly as toxic as ammonia or nitrites, nitrates can be present at lower levels, and still support most marine critters. Ideally though, the lower the nitrate levels, the less stressful the environment is for the majority of the critters we want to keep.

Chemically, it's described as N03-

Why's it Important?
It's a similar concept as with ammonia and nitrites, but a different chemical. The bacteria that consume nitrites produce nitrates as a by-product. The affect of nitrates though, on most inhabitants is less severe, and at small enough concentrations it can be harmless. But at high enough concentrations, the affects can be much the same as ammonia and nitrites. This means stress to the tank's inhabitants, and even death.

In a lot of beginner books, the Nitrogen cycle explanations tend to stop here. However, there is one more step in the cycle. There are bacteria that consume nitrates and as a by product, produce nitrogen gas. This nitrogen gas forms bubbles, and eventually floats up and out of the water. However, the specific species of bacteria that do this only thrive in areas of the tank with very little or NO oxygen (called anoxic areas). This can be really deep inside your live rock or at the very bottom parts of a deep sand bed (DSB). It is for this reason that DSB's and tanks with larger/denser pieces of Live Rock are very good at keeping your nitrate levels very low. But don't take that to mean that DSB's and dense rock are all good. They have their pro's and con's, and while I'm not going to get into them in this article, I highly recommend researching them before making decisions on substrate and LR choice.

For the most part, without larger or more dense pieces of live rock, or a DSB, the affects of this final stage of the nitrogen cycle are less than ideal in a normal reef tank. However, frequent water changes can more than compensate for this lacking.

What Value should I Aim For?
Ideally, you want 0 detectable nitrates. However…most critters can handle anything under 20ppm, fish especially. Corals however can be touchier. Some corals like softies and most LPS can not only deal with 20ppm or less, but are rumored to actually prefer these levels. But the less hearty corals (like SPS's) will do much better as you get closer to 0.

As an aside, Clams LIKE nitrates. But you still should aim on no more than 20ppm with clams, as higher levels can still be toxic. Overall, it's still best to try to keep your nitrate levels as close to zero as possible.

One important thing to note is that algae can be fuelled by nitrates. So while having values under 20ppm is acceptable for most critters, it can lead to other problems down the line, like frustrating algae outbreaks.

What Do the Values mean?
Simply put, the values tell you how much Nitrate is contained in the water. The values for nitrates are commonly given as ppt which means parts per thousand. This means if you broke down the water into all it's parts, for every thousand of those parts, this value is how many of those would be Nitrates.

When Should I Test For It?
Until you are more advance, and really have your tank's husbandry mastered, Nitrates should be tested very frequently. Towards the end of a new tank's cycle, testing daily is not a bad idea. No critter should be added until nitrates are below 20ppm for at least 3 or 4 consecutive days after you get 0 ammonia and 0 nitrite levels.

Once your tank's set up and cycled, testing nitrates on a weekly basis is not a bad idea. Anytime you've changed your feeding schedule, added new filtration/skimming equipment, added a significant new critter, or any other change to the tank's bio-load, more frequent testing for nitrate levels is suggested for a few days after the change.

After you become more advanced in the hobby, you'll get to know your tank pretty well. At this point, you may not need to test as often, or only test when you notice something in the tank is "not quite right". But until this familiarity and advanced understanding of your specific tank's husbandry and reactions are achieved, it is recommended to test for nitrates frequently.

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Alkalinity:

What is it?
(Related to pH) Scientifically, alkalinity is a measure of the acid neutralizing capacity of a solution. I know…a bit wordy, right? But in regards to the marine aquarist, it's simply the measure of the ability of your tank's water to hold its current pH levels as well as a measure of the amount of calcium carbonate (used in the process of building skeletal mass).

The better your alkalinity value, the less likely you are to have pH swings. Alkalinity is also tightly relates to Calcium levels, but we'll get into that later. In the marine hobby, this value is almost always measured in terms of Carbonate Hardness, or KH (not to be confused with general hardness GH, which is the value usually tested for in the Freshwater hobby).

Why's it Important?
Alkalinity's affect on the tank is a big one, but is rather indirect. As mentioned before, it's mainly a measure of Calcium Carbonate, but without getting advanced, it's also a measure of the tank's ability to maintain its pH levels. So indirectly, if your alkalinity is off, then all the affects that pH has on the system come in to play. Bad alkalinity can allow rapidly shifting pH values which in turn will cause bad chemical reactions to take place in the tank.

Alkalinity is also very tightly related to calcification. Calcification really requires a scientific explanation to truly understand it, which is why I include a lot of links going into detail on this subject later on. But in staying with the goal of THIS article, I think it's easiest to also think of it as the ability of the tank's water to hold calcium as well as the critters abilities to utilize that calcium in the water column.

Once the tank's water is super-saturated, Alkalinity and Calcium levels become inversely related. Raising alkalinity can cause Calcium levels to drop, and raising Calcium levels can cause alkalinity to drop. Let me explain this with an analogy.

Let's say you have a normal sized shoebox and let's say you an unlimited supply of red golf Balls and an unlimited supply of blue golf balls. You can only fit some finite number of golf balls in the shoe box, regardless of their color. Initially you can have a few red golf balls and way more blue ones. Then you could add lots of red ones to make the amount more even. You can keep adding various colored balls until eventually, the shoebox will be full. This is when the box has reached super-saturation (fancy word for, "it's all full"!)

Take note that until the box fills up though, there is no correlation between the red and blue golf balls, meaning that adding a blue ball does not affect the number of red balls in the box. But once the box is full (super-saturated), in order to increase the number of blue balls in the box, you are going to have to remove a red ball.

This is what happens with Calcium and Alkalinity in your tank's water column. The water can only hold so much dissolved stuff over all. Once it's full, putting one in the water column can force the other out (precipitation).

At balanced super-saturated levels, corals can more easily pull the calcium they need from the water column, and as a result, can potentially grow faster. However, if the super-saturated line is crossed, precipitation can occur in the tank. This is a fine line to balance when trying to achieve optimal growth rates, and is only suggest for an advanced hobbyist. Achieving super-saturation is not necessary, and as long as Alkalinity and Calcium levels are in an acceptable range, growth will not be inhibited.

What Value should I Aim For?
Anything from 2.5-4 meq/L (7-11 dKh) is acceptable. Actually there is no exact target you should shoot for, until you get more advanced. For the most part, as long as you're in that range, you are providing a good environment for your tank's critters.

Higher alkalinity values than that range, and you can run into problems with precipitation. Basically, this means your water can not hold anymore calcium carbonate (main compound that an alkalinity value is measuring). So, as a result, excess calcium carbonate starts to solidify (much like when you put too much sugar in your iced tea). This excess will begin to accumulate on equipment, forming a crust or shell. This reaction is easier in warmer areas, so it's very common for things like heaters and pump impellers to get a build up on them. In extreme cases, you can even get what appears to be snow in the tank's water column.

Lower values will cause instability in your tank's pH level. This may result in constantly lower or higher pH readings. Or even worse, wild swings in the tank's pH. This causes stress on all tank inhabitants leading to a slow demise, disease, and eventually death.

What Do the Values mean?
mEq/L - means milli-Equivalents per liter.
dKh - means degrees of Carbonate hardness, and is simply 2.8 times the mEq/L value.

Both of these are chemistry terms which to truly explain them would require chemical explanations that are more advanced than the purpose of this article. I've included links that go into more detail about each later in this section, but for now, let's just think of them as units of measure for alkalinity.

When Should I Test For It?
Whenever your having problems with or trying to maintain your tank's pH, Alkalinity, or Calcium levels.

If you're trying to keep calcifying corals (corals with a skeleton) and are trying to maintain good growth conditions, testing for alkalinity is a must.

Anytime you are dosing in any fashion in an attempt to affect pH, Alkalinity, Calcium, Magnesium, Strontium, etc levels, monitoring your Alkalinity levels is highly suggested. At least until you become familiar with it's affect on your tank.

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Calcium:

What is it?
Easy one…It's the amount of calcium (Ca) in the water.

Why's it Important?
Calcium itself, is used by the animals in the tank mainly to expand their skeletons (i.e. grow). Calcium is also inversely tied into alkalinity. If calcium levels drop, alkalinity will normally rise, and vice versa. Balance of the two is the goal. Please review Alkalinity prior to reading this, as Alkalinity and Calcium are tightly related to each other.

What Value should I Aim For?
Anything in the range of 380-450 ppm is good. Again, until you get more advanced (especially when trying to maintain SPS corals), any Calcium value in that range is acceptable.

What Do the Values mean?
The test values are usually in mg/L or ppm, which are interchangeable.

mg/L - means milligrams per liter
ppm - means parts per million

Both are equal units of measure and they both mean how much calcium is contained in the solution.

When Should I Test For It?
Testing Alkalinity or Calcium levels alone don't do much good. Both must be tested together to get a good picture of what's going on. Therefore, the answer here is the same as with Alkalinity.

Whenever you're having problems with or trying to maintain your tank's pH, Alkalinity or Calcium levels.

If you're trying to keep calcifying corals (corals with a skeleton) and are trying to maintain good growth conditions, testing for calcium is a must.

Anytime you are dosing in any fashion in an attempt to affect pH, Alkalinity, Calcium, Magnesium, Strontium, etc levels, monitoring your Calcium and Alkalinity levels are highly suggested. At least until you become familiar with it's affect on your tank.

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Magnesium:

What is it?
Another easy one… the amount of magnesium (Mg) in the water.

Why's it Important?
Again, to get a true understanding of Magnesium, a more chemical explanation would be beneficial. But for simplicity's sake, think of Magnesium as a Calcium wanna-be. During calcification, occasionally, Magnesium can be chemically substituted for Calcium. This means higher Magnesium levels can allow more calcification (a.k.a. growth) to occur. There are side affects for extreme levels (too low, or too high).

What Value should I Aim For?
Anything from 1250-1350 ppm is a good goal for Magnesium levels. The BEST value for you Magnesium is roughly 3 times the amount of Calcium in your tank's water.

Very little is known about the affects of magnesium levels that are extremely low or extremely high. As for the importance of Magnesium levels in general, there's not much we can tell you without going into a lot of detail requiring a good knowledge of chemistry. My suggestion is to either not worry about it (as it's very rarely the cause of common tank problems, until you get into more advanced set-up), or simply just aim for the range specified. An advanced article on Magnesium has been included in the links at the very end of this FAQ section. Feel free to view it for more detailed information.

What Do the Values mean?
The values tell you the quantity of Magnesium in the water in parts per million. This means, if you broke down the water into a million pieces, how many of them would contain magnesium.

When Should I Test For It?
This is mainly an advanced test requirement. However, if you are dosing your tank with Kalkwasser, testing for Magnesium levels once every week or two isn't a bad idea. Kalkwasser helps maintain Alkalinity and Calcium levels, but one side affect is that Kalk use can cause slowly depleted Magnesium levels in the water column. Frequent water changes can compensate for this though.

Also, if Alkalinity levels and Calcium levels are right where they should be, and you're still having problems with coral growth or pH, depleted Magnesium can be part of the problem. This is rare, but possible.

There are also theories that suggest low magnesium levels can allow cynobacteria to grow more easily. I'm not 100% sure of this, so I'll say no more on the subject, but if this becomes a problem for you, I recommend further research on this concept.

The main need to test for magnesium comes for advanced aquarists who are trying to get accelerated growth rates out of SPS corals. Other than that, sufficient and frequent water changes should keep your tank's magnesium levels right where they need to be.

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Total Dissolved Solids (TDS):

What is it?
It's just a measure of how much organic AND inorganic content there is in the water. Or, in other words, how dirty (how much unwanted stuff) is dissolved in the water.

Why's it Important?
TDS is a measurement that applies only to the freshwater you use for topping off and mixing new salt water. TDS is a measure of how dirty the water is. The dirtier the water, the more harmful it can be for the tank. In relation to TDS, dirty water means unwanted metals/minerals which can be toxic to the creatures in your tank, as well as excess nutrients that can fuel pesky algae outbreaks. The cleaner the water the less impurities you're adding into your closed system.

What Value should I Aim For?
Since this is mainly a measurement used on the water you'll be using to mix new SW or to top off with, ideally, the closer you get to zero, the better for the tank. RO/DI units can get your water down to zero. Tap water (depending on where you live) can be anywhere from close to zero (rare) to all the way up to 300 or more TDS. Since TDS is basically a measure of how much "stuff" is in the water, it makes sense that the less stuff there is the better.

So ideally 0 or as close as you can get to that.

What Do the Values mean?
TDS is an estimated count of how many dissolved solids are present in a unit of water.

When Should I Test For It?
If you have an RO/DI unit, depending on how much water you produce, you should test your output water every 30 or 40 gallons produced. Some units come with TDS meters that allow you to test constantly.

Readings of higher than 5 TDS are probably cause to replace your filters. Some, like myself, even argue that readings higher than 1 TDS are sufficient to prompt a filter change.

If you do not have a RO unit, you may want to test your tap water for TDS to determine the need to get one. It is NOT uncommon for tap water to have TDS readings of 200 or much more.

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Phosphates:

What is it?
A measure of how much Phosphate (PO4) is in the water

Why's it Important?
Phosphates are another tricky subject. Again, trying to keep it simple for the purposes of this paper, phosphates are fuel for algae. High phosphate values will end up meaning large algae growth. High phosphate content also can impede calcification (skeleton building). Phosphates do not really affect fish and inverts, and are mainly of concern when having problems controlling algae, or getting good coral growth.

What Value should I Aim For?
Phosphate values as close to zero as possible are ideal. The problem is, most commonly available test kits out there don't do a really good job of testing true phosphate levels in the tank.

Phosphate is always present in the tank though. It's simply a matter of keeping these values as low as possible. The main problem with monitoring phosphate levels is that the majority of phosphate in your tank are consumed by the algae, and therefore are bound into the actual algae itself. This means that most test kits will not take the bound up phosphate into consideration. (I.e. You can get readings near zero, but still high phosphate content in your tank. The majority of it, inside the algae).

Again, I've included articles with more information on the subject. For the most part though, good tank husbandry (cleanings, water changes, controlled feeding, good skimming) will keep your phosphate levels in check. If you start developing severe algae problems, more research on the topic is recommended.

What Do the Values mean?
The test values are usually in mg/L or ppm, which are interchangeable.

mg/L - means milligrams per liter
ppm - means parts per million

Both are equal units of measure and they both mean how much phosphate is contained in the solution.

When Should I Test For It?
When fighting algae outbreaks and also when experiencing unexplained sudden coral bleaching/recession/death.

Testing weekly can be done as a preventive measure. But I urge research into the specific brand of Phosphate test kits you decide to buy. Not all phosphate test kits out there give results that really mean anything.

Phosphate Testing and Removal
from Salifert Test Kits
<a class="postlink" href="http://www.salifert.com/pt/po.htm" onclick="window.open(this.href);return false;">http://www.salifert.com/pt/po.htm</a>

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Iodine:

What is it?
Iodine is a general term and actually is comprised of many types and parts [iodide(I), iodate(IO3), organic, inorganic, molecular iodine(I2), hypoiodite, etc]. Most test kits provide a value that is a not specific to any one, or an overall collective value. The problem is each form may have different purposes in the reefs, and unfortunately, very little is know for sure at this point.

Why's it Important?
Iodine is a trace element found as a very small percentage of Seawater. It is used and produced by a variety of critters for a variety of reasons. It is still an area that is being researched constantly by marine biologists, and as a result, very little about iodine content in our tanks has been proven one way or the other.

As I stated earlier, Iodine is actually is comprised of many types. Some of which are misleading or useless for the purposes of our hobby, almost all of which are currently in debate.

In general, Iodine content in the aquarium is an advanced subject by its very nature. I will not go into much detail on it, but have included links to some interesting (albeit somewhat advanced) articles on Iodine at the end of this FAQ section.

One final comment I will make about Iodine is, since it is such an advanced and currently fluid topic itself, I strongly urge that maintenance of this parameter be left to advanced hobbyists, and that thorough research is done before trying to adjust Iodine levels.

What Value should I Aim For?
Iodine is found in Ocean water at values around 0.06ppm. Trying to maintain this level manually is not recommended. Because it's a trace element, it is better to leave maintenance of this parameter up to your Salt mix and frequent water changes. Extremely high Iodine levels can lead to increased molting of crustaceans (thus shortening their life spans) and in general, can be toxic to your tanks inhabitants. Trace elements in general really shouldn't be messed with. Because of how small a percentage of SW they make up, any manual tinkering can yield rather extreme shifts in these values. As with all parameters in this hobby, extreme shifts in anything usually have detrimental affects on the tank.

What Do the Values mean?
Iodine test results are frequently measured in ppm, or parts per million.

When Should I Test For It?
You really shouldn't. Trying to maintain iodine levels in the tank is not recommended, and should be left to advanced hobbyists. Most reported benefits of iodine dosing are anecdotal and very little scientific proof has been given. There are definite bad affects of iodine overdosing though. So while there may be some benefit, given the potential damage, until more is known, it's best left to the experts.

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Copper and Other Trace Elements:

What is it?
There are many other chemicals you can test your water for, each a measure of that chemical. Most are not important, other than that they remain trace (very minute amounts) elements in proper proportion. Some of these are Copper, Strontium, Iron, Silicates, Boron, etc. I won't go into much detail about these, other than an overview of them all, and an explanation of why you won't really have to worry about them most of the time.

Why's it Important?
The importance of other trace elements is also an area that scientists are constantly studying and discovering. Most do serve a definite purpose, but they are contained in such small amounts that monitoring and maintaining these values are not recommended.

What Value should I Aim For?
As previously stated, it is not recommended that the average aquarist monitor nor maintain these values. But for the sake of interest, I've included a few trace elements and the values typically found in natural sea water:

Chemical Content
Boron Around 4 ppm
Copper 10-40 ppm (parts per billion)
Iron 0.005 ppb (parts per billion)
Strontium typically less than 10 ppm
Silica anywhere from 2.7 to less than 0.06 ppm

Let's take a second, and look at Copper, specifically. As stated above, natural seawater contains extremely minute amounts (between 10-40 ppb - parts per BILLION). While copper may play an important role in the reef's health, it also should not be tinkered with in our tanks. Higher than normal copper levels can be extremely toxic for the tank. Corals and inverts are very susceptible to copper poisoning. This doesn't just mean cleaner shrimps, starfish and urchins. It also means the majority of critters that make your live rock "live" (bacteria, copods, detritus eating worms, etc). Increased copper levels can actually crash a tank and permanently prevent most life from ever doing well in that environment again.

That said, it is HIGHLY recommended that copper levels not be maintained manually in a reef tank. Also note that most fish medications for Ich and other bacterial infections contain high levels of copper. Please be aware of this when purchasing and using these medications. It is strongly suggested that these medicines be used in a quarantine tank outside of your reef's water system.

In general, while not as toxic as copper, all the other trace elements are not recommended for monitoring and maintenance either. All for very similar reasons.

What Do the Values mean?
N/A

When Should I Test For It?
I don't recommend you test for them at all.