I concur with other members on the partial water change that is significant, say 65-75% of the tank volume. No one mentioned the reason this usually works, so I will just add that it replicates the start of the wet season when the rains cause the water courses to flood the surrounding forest often for hundreds of kilometers, and sometimes several meters deep. This allows the fish to move into areas that are ripe with food--insects and insect larvae in particular--as well as protection from all the natural terrestrial vegetation for eggs and fry.
I didn't mention the cooler temperature aspect for two reasons. First, it is likely the expanded food availability has as much if not more to do with it. But second...we all used to be told about cooler water, and it generally seems to work, but perhaps only because of the previous aspect (more food area). Somewhere recently I read that warmer water may actually be preferable, because studies have shown that the rain warms as it falls through the hot air and humidity, and the ground is warmer due to the decaying organic matter that covers it for meters, which warms the water pooling on it. I'm not certain, but this may have been Ian Fuller's advice related to spawning difficult Corydoras. If I come across the data somewhere, I'll try to remember to post here.
