How To Breed Corydora

Mine Bred in a Planted Community Tank (90g).
I can't recall my water's temp (more than likely 78F) but the Ph was steady 6.0 and the foods were Flake and Frozen.
They'll typically breed when there's a drop in the water temp after doing a partial (ie 45-50% partial and refilling it with water that's 2-3degrees lower in temp than what the tanks normally kept at- rainy season).

We have fry eggs!! Cory / corydoras baby fish

 

They will also breed if the the weather changes dramatically. Like spawned last week when it was cold one day then hot the next. If you want them to spawn then do a pretty big partial while in the middle of a thunder storm.
Also feeding them meaty foods right before the water change may help.

But you have to be sure you have males and females =P Females will swell with eggs and there mouth won't quite touch the sand. Males on the other hand will have a less fat look. You can also look at them from the top; females will look fat, males slim.

Another thing, are they the same species? I keep two different type in my tank, one I have only females and the other is more males than females. They don't hybrid vary easy, so keep that in mind.

 

My close buddy breeds them and dwarf pleco's. We have found that a 5 degree lower temp difference (up to 8 degrees), fresh rain or RO water is all you need, He breeds his in rain water during the wet months and I feed him RO water during the frozen months here. We have even used melted snow and that has done the trick as well, but 5g of snow is about maybe an inch or three of water in the bottom once thawed.

Corydoras are easy to sex, females are the big ones and males are the smaller ones, more streamlined. females only bulge right before spawn. I stopped mine from messing up my display tank with scattered eggs by bring in fresh water that is identical to the temps I have in the tank now.
They will hybridize in a multi species tank as well.

 

When we had Corydoras panda in a smaller tank, where we could control them more and nobody was eating their eggs, they bred when the water temperature dropped - because, in the nature, they breed during the raining season, when the water is cooler and fresh. We used to change about 30% of the water (it was a 15 gallon tank, so it was not much) for water from tap, which we left for 24 hours before adding into the tank, in a open bucket, so all the chloride could evaporate. The water change also cooled the water.
They also like blood worms and many times they had them the day before they bred.
Now we have corydoras in community tank (100 gallon) with lot of other fish, we do not change the water and they bred anyway. I do not know how often and if they still bred, but one of our mature corydoras was born in the new tank.

 

you don't do partials on the 100g? if not, just because it's a bigger tank with more water volume doesn't mean water changes can be skipped...if you don't already have it get yourself something like the aqueon water changer or python no spill clean n fill system (they're great)