aggression of fishes

Question
hi.my tank is doing well. i am changing 20% water change every week. now the problem is in last 7 days sucker(scavenger), small albino gourami, kissing gourami has been eaten by other fishes. i am not sure who starts attack among red tiger Oscar,blood parrot,red belly paku. should i keep light on for all the time or switch off in the night. thanks.

Answer
The problem with your tank is compatibility.  The Oscar and Pacu will devour any fish that can fit into their mouth.  The blood parrot will get bullied as they get older.  It's got nothing to do with lights.  Its all about their inherent aggression behavior.  The Oscar cannot be housed with anything smaller than it.  The Pacu is extremely aggressive.  You need to decide which fish your going to keep, and which ones you're going to give away.  You're not going to be able to keep them all.  Sorry.