I have a Maxi-jet operating in power head mode that is 160 gph. That is 8x my 20 gallon and I think its alot but my fish tolerate it well. I removed it on Sunday after a little maintenance and it took all day for the tank to ALMOST clear. I wanted to leave it off but I need that flow to be happy. I wanted a Maxijet 400 but they were out of stock.