I've recently got a goldfish and I have a few questions on giving it a happy life.

1) I was told that my fish can get lonely in it's big tank all alone, and that I should place a mirror close to and facing the tank to keep him from getting depressed, I don't really see him caring, but would it help?

2) I have the basic lighting my tank comes with and that obviously makes my tank and fish look a lot better, but is it bad to leave the light on for too long? Will it mess up some kind of sleep or feeding cycle for my fish? I have a small pothos in the tank to help keep it clean and give my fish a place to hide, will the light being on too long cause extra mold when combined with the plant?


3) If I eventually add a tank mate, are those black algae eaters that stick to the tank sides ok, or will one end up terrorizing the other? (Or eating my plant, no good...)