From what I have read there has to be a dramatic drop in water level and temperature and you should also be feeding them frozen and live food. I've had my corys spawn once and it was by accident. I had decided to move my 55gal out of my living room into the new fish room so I had to transfer all the fish to a bucket and drain all the water and then fill the tank back up once it was moved. The fish had to be in the bucket for several hours. The next morning I woke up to eggs on the glass. Most of the eggs had been eaten already by the betta(sticky stuff was still stuck on the glass) so I scraped the rest off with my debit card, put the eggs in a container with water that was floating in the tank, plopped in and air stone and all the eggs hatched a little while after. Fed them crushed flakes when they were tiny.