They say that pygmy corys (Corydoras pygmaeus) are easy to breed. That is, of course, a relative statement. "Easy" relative to what? But at this point, doing so is one of my primary goals.
In general, in order to breed corys you need frequent water changes coupled with a "conditioning" diet. They conditioning diet is a rich diet - often with a lot of live food, and essential fatty acids - that bring the fish into breeding condition. Water changes, on the other hand, mimic the beginning of the wet season, when streams and pools get an influx of fresh water. Fresh water, often cooler (although people have said that "cooler" is not important for pygmy corys).
The tank the corys are in is open-topped. As a result of this, evapouration rates are high. Over the last several months, this has meant that I am more inclined to add water than I am to exchange water. Presumably that resulted in very hard water - not the optimum for these fish. So over the past few weeks I concentrated on getting the water closer to tap water, but doing frequent, large water changes. Over the last week I have tried to soften the water some more by adding reverse osmosis water.
The pygmy corys have responded fairly well to the water changes - they seem much more active the past few days, although they still spend most of their time hidden below the dense lawn of Hemianthus. I'm cautiously optimistic.