Sump

[Chase31]

so looks like i will be getting a roughly 600gph overflow, so im looking for a pump, preferably the cheaper the better (will be looking on Kijiji) the head pressure is about 5 feet, it shouldnt matter if its under my overflow right? the system should be about 40G with sump and piping and skimmer when all's said and done witch is about a 15x turnover rate per hour, thats pretty good right? should it be higher or lower, dispaly is 31 gal, sump is 10, also getting a 175 GPH aqua clear power head