Try reading under discussion /General/Do goldfish mind algae in their tank?
I always belief good water quality is about good water management. Is mainly about bringing the waste level down. Most filter take care of the solid waste and the bacteria in it normally breaks it down to nutriens. Just because there is no debri doesn't mean the water is good. Some form of element should be managing the nutrien built up before it reachs to a poisionous level. It can be human intervention (changing of water) or by nature (choosing the correct plant). the best is combination of both. Hope it helps you.