Hello, I really appreciate all the great advice you have given me!! I am now facing the next dilemma. I have purchased 2 Rubbermaid Agricultural 300 gallon stock tanks. I intend to use them side by side in my basement to keep freshwater Stingrays. I am at a loss as to what to use for filters. I know these fish demand excellent water, and am prepared to do lots of water changes with RO/DI water. What type of filters should I run? I have heard these fish very sensitive to nitrates. Too bad they are freshwater instead of marine or I could just use live rock. What is the answer for nitrate reduction in freshwater besides water changes?