Add Homonym wrote:

Having the lights off for a couple hours will lower the fishes
metabolsim a bit. That might make them less aggessive, or might not.

I've had two fish that tended to get more aggressive when the lights went out.
One was *very* bad. That was an Imperator Angel. He would wait until other fish
went to sleep and then attack them. He killed hundreds of dollars worth of fish
in my tank. I finally traded him in for store credit.

George Patterson
Forgive your enemies. But always remember who they are.