Filter Flow & Turnover Calculator
Turnover is how many times per hour your filter cycles the full tank volume. Pick your tank type, enter your filter's rated GPH, and see whether its real-world output actually hits the target.
Manufacturers rate flow with no media and zero head height. The AquaLens app applies the same ~35% real-world reduction when it evaluates your equipment, so the comparison here matches what you'd see against your actual tank.
Why rated GPH overstates real flow
The gallons-per-hour number on a filter box is measured under ideal lab conditions: empty chambers, no filter media, and zero head height. In a running aquarium, media restricts flow, biofilm builds up between cleanings, and canister filters lose output pushing water up to the tank rim. A realistic estimate is around 65% of the rated figure — a "300 GPH" canister typically delivers closer to 195 GPH once it's actually filtering. That's why sizing a filter to exactly match the minimum turnover usually leaves you short.
Turnover targets differ by bioload and tank style. A lightly stocked freshwater community does well at 4–6× per hour, planted tanks benefit from 5–8× to move CO₂ and nutrients, and goldfish or other messy eaters need 8–10× to keep up with waste. Reef numbers look wildly higher (20–40×) because they describe total in-tank circulation — powerheads and wavemakers included — not just filtration. The AquaLens app tracks your actual equipment and applies the same real-world derating automatically.