i know this is a stupoid question... generally i make sure i have an obscenely powerful filter in all my tanks.but what i wanna know is roughly how many times a filter should turn over a tank in an hour? thnx

just relised u put this in the wrong place sorry

that would depend on the type of filter you are using. for hob style filters a turnover ratio of 10 x is the norm, with a canister type you should be looking for about 5-6 and for a sump system somewhere around the 4-5 mark

i have 2x fx5,s on a 170 uk gal tank ......

A lot of the time the rates a manufacturer quote are maximum output cos that sells the filter. the fx5 is rated to 400us gallons but a few of us run 2 of them on 150-200g tanks. for me this gives a few benefits, main being if one goes wrong my filtration isn't lost, as i have backup. cleaning time is less, i clean my filter ( 1 ) every 4 months, last I hate particles floating around. necros rates are a good.