Crush (aka Fat Fat) is about 17 years old (picture attached) and he has a 75 gallon tank with a Fluval FX4 canister filter. The filter is less than a month old and I did 1 partial water change (about 75%) on this last Friday (3 1/2 days ago) because the water was so green and becoming smelly. And it had only been about 2 1/2 weeks since I had put in the filter. I cannot keep the water clean. It's perpetually yellow/green and I'm not sure why

