most of us average 1000 - 1200 gph flow thru each 55 gal barrel. 3 minutes is adequate for a decent biological hangtime... and the more flow the longer particles stay in suspension.working their way up into the biological media. 1000 - 1200 gph is a happy medium, it allows over 3 minutes in filtration and the flow is light enough to allow for a good settling of debris in the filters sump area. using a larger diameter pipe to plumb your filter aids in this as well.allowing more flow , but under less pressure, so debris can settle faster, before reaching the media. i use 1&1/2" pipe to plumb mine.