I have been do alot of research lately before I build my own filter system. I want to build a diy (do it yourself) canister or wet/dry filter. However in all the pages I have read, I can not find a constant calculation between gph and tank size. I know this can vary greatly depending on the amount of tubing between the filter and your tank. Also the height of the pump compared to your inlets and outlets. But there has to be a way to calculate the gph needed to filter any given tank size with the variables considered. Help!