Net water, not tank rating. Use the Tank Volume calculator if you have not measured it.
Total in tank flow against what the corals you keep actually want.
Above the range. High flow rarely harms SPS but it does sandblast the substrate and irritate LPS. Point pumps at each other or at the glass, not at corals.
turnover = (1,514 + 11,356 L/h) ÷ 283.9 L = 45.3×/h
Turnover is total flow divided by volume, and it is a rough guide rather than a specification. A tank with 40 times turnover all running in one direction has worse circulation than one with 20 times set up to collide and swirl.
What corals need is variable, chaotic, and reaching everywhere. Two pumps pointed at each other build a random pattern. One pump on full blast builds a dead zone behind the rock.
The ranges here come from what reefers report working, not from a controlled study. Softies and mushrooms want the least, SPS the most, and everything else sits between.
The return pump is not a flow device. Sizing it to hit a turnover target makes the overflow noisy, gives the skimmer less contact time, and burns power around the clock. Five to ten turnovers through the sump is enough. Powerheads do the rest at a fraction of the running cost.
Signs of too little flow: detritus settling in corners, cyanobacteria films on the sand, coral tissue receding on the shaded side. Signs of too much: corals permanently closed, sand blown into drifts, fish struggling to hold position.