+1 on the discus comment. Happened to me too! :thumbsup:
I hope this is a joke, because there is no regularly timed geological activity that fish can use as triggers to breed. Fish use rainfall (not as much in reefs, but it does happen) as a "signal" to know spring is here. That corresponds with a rise in temperature, and the rainfall brings down more live food. When that all happens together over the course of a few days, fish know it's time to breed.