I have a pacu thats pretty good size in a 30 gal. tank all by himself. i know that i can't plant it b/c he'll eat them, so my question is how do i keep the water from turning green? i do a 20% water change every week and it still looks nasty! i have a bio filter that i haven't touched and i have a powerhead for circulation b/c he chewed holes through the tubing for any type of bubbler.