What are the differences between keeping a freshwater and saltwater aquarium? It has often been said that saltwater tanks are much more challenging and difficult to maintain, requiring a lot more work. I'm here to confirm that this statement about aquarium cost and maintenance is absolutely true. Before you allow yourself to be seduced by the rich colors of saltwater environments, the large variety of livestock and the fascination of corals, be very sure you understand how much additional knowledge, cost, time and work you'll need to dedicate towards maintaining a saltwater aquarium. But if you do decide to make the effort, the results from a saltwater or reef tank can be astonishing.
Water Purification, Water Changes and Salt Requirements
Let's start with the most basic maintenance item for any aquarium - water changes. For the most part, adding, removing and replacing water in a freshwater environment is simple and painless. You can use plain tap water from your home faucet and add a few drops from a dechlorinator (chlorine remover) such as Seachem Prime or API Tap Water Conditioner. The chlorine remover (and frequently ammonia) can come in very small, efficient bottles and will last you for months and probably an entire year.
There is no such ease with saltwater. Unless you have special equipment, tap water cannot be used to mix with salt. Reverse Osmosis De-Ionized (RODI) or distilled water must be used. RODI units can be are large and very expensive, typically costing several hundred dollars. I use distilled water which I purchase every few weeks from our local supermarket.
RODI or distilled water must be mixed with a special sea salt, which usually comes in very large bags or containers. Care must be taken to ensure that the salt level in the water is roughly 1.022 - 1.026 parts per thousand (ppt), also known as Salinity or can also be measured as something called Specific Gravity. The actual level you need can depend upon the temperature of your water.
Determination of salinity is accomplished by using a tool which every saltwater aquarium owner must purchase - a hydrometer or a spectrometer. A good spectrometer (preferred by reef owners) will cost no less than $25 and a quality unit can easily exceed $75-100. Cheaper spectrometers can be hit or miss and also do not contain "calibration" fluid which is used to test your equipment and ensure that your levels are accurate. The 10-15 minutes doing a water change for a freshwater tank took me easily 15-20 minutes with saltwater and longer if I didn't have enough saltwater already mixed.
Maintaining Water Levels and Salinity in your Tank
If the water level in your freshwater tank drops, there is no need to panic. The fish and plants are usually unaffected by a small 1-2 inch drop in the water level of a tank that is usually at last 10 inches tall. To remedy the issue, simply add dechlorinated water back into your aquarium to the desired water level.
Let's assume you've mastered the saltwater salt mixing basics. An additional challenge is maintaining the water level because you also need to maintain salt levels. But if you just add more saltwater to your tank in the same fashion as freshwater, you'll end up killing all your corals and livestock. The impact isn't obvious and here is how freshwater and saltwater tanks truly differ from a maintenance perspective.
With saltwater tanks, water evaporates but leaves salt behind in the tank. You'll see the dried salt deposits left in various places. Over time, the salinity level in your saltwater tank will rise because while a good deal of water has evaporated out of the tank and into the air leaving the same salt concentration to a lower amount of water. Caked salt deposits are frequently washed back into the aquarium water, adding even a higher concentration of salt to water. You need to add RODI or distilled water back into the aquarium - without salt - in order to maintain the proper salinity level. Unless you plan on adding another larger reservoir near your tank, you'll need to manually add RODI or distilled water at least every other day in order to maintain reasonably proper salinity levels.
Aquarium / Tank Size for Freshwater & Saltwater Aquariums
There are no practical limitations on freshwater aquarium size. Small tank sizes will require more frequent water changes in order to deal with the build up of impurities and waste products in the water. A 5 gallon tank requires water changes every few days, a 10 gallon tank weekly and a 20 gallon or larger can vary between a week or bimonthly.
The need to maintain proper salinity levels translates into a seeming paradox - larger saltwater tanks are much easier to maintain over the smaller variety. This is because the impact of water evaporation on a tank with a small amount of water will greatly impact on the salinity level which can dramatically increase. Saltwater "pico tanks" (about 5 gallons and under) and "nano tanks" (roughly 6 to 30 gallons) are considered small. Only experienced saltwater aquarium owners should try to maintain a pico tank. I'd probably suggest that beginners start with a tank no smaller than 20-30 gallons for reef or FOWLR (Fish Only With live Rock) aquariums. These will be much more forgiving.
Equipment - Saltwater Lighting can be Complicated, Expensive
Lighting for freshwater tanks is usually very simple. Most tanks come with canopies and fluorescent bulbs which are just bright enough to be appropriate for the tank size and minimize algae growth. If you've got a "planted tank" which includes live plants, you'll need to approximate needed lighting levels, such as approximate watts per gallon. With standard sized tanks there are often relatively modest options that should be sufficient.
Saltwater tank lighting can be extremely complicated as there are a large variety of types, each with different benefits and detriments. There is no reliable way to go the truly "cheap route" when lighting corals. You can expect a decent saltwater LED bulb for corals to cost you at least $70 just for the lighting itself and more for the fixture. This is because bulbs with the proper lighting spectrum are not as easy as you might expect to find. Pico and nano tank lighting is often built into custom nano aquarium kits commonly referred to as "cubes" since many are shaped as close to the dimensions of a cube.
Most standard lighting is constructed for 20-30 gallon tanks and larger. If you're operating a 20 gallon or larger reef tank, expect to spend at least $100 and more likely $150-200 on quality lighting that allows for flexibility such as lighting spectrum, intensity, dimming and also night versus day lighting. Most common is to have a ceiling mount for lighting which allows for a base unit to hang on a string or chain roughly 10-16 inches above the top of the tank.
Equipment - Saltwater Tanks can Require Many Extras
Freshwater tank setup is relatively straightforward. You need a tank, gravel and rocks (optional), plants and decor (optional), basic lighting (which usually comes as part of a cover or canopy), mechanical filter, heater, thermometer, air pump and stone, net, glass scraper/cleaner and water siphon (optional). If you intend to go higher end, you might need a little more space for a canister filter and add media for chemical and mechanical filtration. Your costs shouldn't exceed more than $10-30 monthly, at best. You'll also want to purchase some type of fertilizer and perhaps a CO2 unit, many of which are DIY or "Do It Yourself" carbon dioxide devices.
Unless you're running a small pico or nano tank, you will likely need to plan for a large amount of space for additional equipment in order to maintain the health of your marine or reef environment. You'll require most of the freshwater aquarium requirements, although some components will be swapped out with different or more high end equipment.
Many reef aquarium owners have an extra tank called a "sump" that is used to maintain various levels in the main reef or saltwater tank. Even assuming you don't have a sump, you will probably need a protein skimmer to manage chemical filtration. They are highly advised in saltwater tanks. The good ones begin at roughly $120 and I've used the Tunze 9001 Protein Skimmer with good success. If don't need one, you can use mechanical filtration along with chemical media and more frequent water changes. Saltwater tanks may also require an automatic top-off device which holds a few gallons of water to deal with the water evaporation issue we discussed above. Otherwise you're manually adding RODI water every 1-2 days. You'll also want to have a water circulator or wavemaker to make sure that there is plenty of motion in the water, which simulates the movement of the ocean.
Livestock - Saltwater Fish and Corals are Expensive, Have Limitations
If you've become enamored of the beauty of reefs, be very aware that corals and fish are usually much more expensive than freshwater livestock. And the real issue with saltwater fish is that even small fish will typically require a large aquarium. A freshwater betta fish will enjoy the room in a 5 gallon tank. But add even a small chromis or damselfish to a saltwater tank and you'll be surprised how territorial these fish can be even at small sizes. Sand sifting gobies usually require tanks that are 20 gallons and larger at minimum - and that really is the absolute minimum size. Unless you can find the right mixture of fish at your local fish store, you'll be very limited with what you can keep in a nano tank.
The cost of saltwater livestock are usually a multiple of freshwater. Unless you have a large tank, you will be limited to what is appropriate for your tank. A friendly shrimp such as a Blood or Scarlet Skunk Cleaner Shrimp can easily run you $20-30 per shrimp. Contrast this with a freshwater cherry shrimp which should run at no more than $5 per shrimp. Ghost shrimp are almost always available at no more than $2 per shrimp. And considering that the large variety of saltwater issues can result in the death of livestock with more frequency, be prepared to be surprised when the costs skyrocket.
We haven't even discussed coral costs. While you can get "frags" or fragments of larger corals at only $15-20, these will take a good deal of time to grow. And often they will die, fade or not thrive, leaving you out the money and nothing to show. Larger corals of a size that might impress will usually begin at no less than $30-50 per coral, such as ten zoanthids or palythoa.
Food / Feeding Differences Between Freshwater & Saltwater
Fish and livestock may be carnivorous, herbivorous, or omnivorous. The overwhelming majority of freshwater fish and livestock will eat nutrition enriched flake food, pellets or freeze dried worms All of these foods are are easy to find. If you want to treat your fish well and achieve maximum health and beauty, live bloodworms and frozen brine shrimp are an option. A minority of freshwater fish will require a special diet.
Saltwater fish and corals can be extremely selective when it comes to food and the needs of a small tank diverse. Very few saltwater fish are herbivorous and a good number will refuse to eat dried flake or pellet food. It is important to research the feeding requirements of your fish and your corals. This can include a diet of phytoplankton, brine shrimp, mysis shrimp, rotifers and other food. Most healthy saltwater tanks also exhibit the presence of tiny bugs called copepods and amphipods which these fish may feast upon. You'll want to be very careful with understanding what feeding requirements are necessary for the inhabitants of your saltwater or reef tank to thrive.
Setting Expectations is the Key to Aquarium Success
Appreciating expectations will result in the great success of whichever type of tank you choose to maintain. Please don't be discouraged by all the additional requirements of marine tanks, some of which can vary once you've mastered the learning curve. But the payoff from understanding the complexity of saltwater and reef tanks can result in a most beautiful, enjoyable, fascinating and interesting experience.
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Freshwater v. Saltwater: Cost, Maintenance, Equipment
A comprehensive explanation of cost, maintenance and equipment requirement differences between freshwater and saltwater tanks.
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