depends on the tank and whats in it (lots of fish that produce a lot of waste vs a few fish that dont produce much waste vs a tank with mostly plants vs whatever)
general rule is something like 3-8 turnover per hour
so for a 50 gallon tank.. thats anywhere from 150-400gph..
not only is gph important but how the water moves also plays a roll... if you fish are getting blown around and all your plants are getting uprooted thats no good..
theres not really any such thing as "overfiltering" a tank.. but you can end up doing more than you need to
Im kinda in the beginning stages of a pretty crazy DIY project. I want to make a plywood and glass tank inside of a big screen tv, i would like to make a sump filter for it underneath the tank where the speakers for the tv go. So im trying to get alot of info on everything before i start so i know exactly what im getting myself into and what its going to cost. thanx for your help
I like to stick with 5X turnover or more, but I use to run my 2 - 55 gallons with an Emp 400 on each and the water was always crystal clear. My 220 I have an 1800GPH pump (probably around 1500 with loss) and an FX-5 on it. My 8 Foot (240-250 gallons) will be set up the exact same. The 150 will jst keep the FX-5 (This is rather low imo but it is a single fish). Also the 125 will get an FX-5 on it soon (single fish also). I think you can get away with 3X, I just prefer 5X or more.