Hello! I have recently upgraded to a 55 gallon tank and was wondering how often and how much water I should change. I have 4 fish, a blackmoor, a ryukin, a baby lionhead, and a comet. I have a emporer 400 gallon per hour filter that says filters up to 90 gallon tanks. There's also a few small plants in the tank, if that makes a difference. Any suggestions would be appreciated!