i have a 90 gallon tank with 2 oscars, 6" and 8", 2 red devils, 5" and 7", a spotted gar, 14", red tailed catfish, 7", jack dempsey, 5", and green terror, 4". I have 2 aquaclear filters made for 50 gallon tanks, and one penguin 400 filter, made for 70 gallon tank. i saw a good deal on a fluval 405, and dont know if i should get it. my nitrate levels are always very low.