I have had discus in a community tank with substrate. Due to a paired couple laying eggs quite frequently, I decided to put them into a breeding tank. This tank only has a sponge filter and no substrate.

The problem is that the male is freaked out by his reflection in the bottom of the tank. He is constantly tilted to one side waiting for his reflection to move and when it does he goes into a frantic panic.

Any suggestions on how to sort this out?