equipment
Filter turnover calculator
Turn a filter's rated flow into real turnover, allowing for the media and head loss the rating ignores.
3.6× per hour in practice (rating suggests 6×)
Suits a general community tank
Working — every step, so you can check it
- Nominal turnover
- 600 ÷ 100 = 6×/h
- Realistic flow
- 600 × 0.8 × 0.75 = 360 L/h
- Realistic turnover
- 360 ÷ 100 = 3.6×/h
Formula
- Nominal turnover (×/h) = rated flow (L/h) ÷ tank water volume (L)
- Realistic flow (L/h) = rated flow × (1 − head loss fraction) × (1 − media loss fraction)
- Realistic turnover (×/h) = realistic flow ÷ tank water volume
Assumptions
An estimate whose assumptions are invisible is indistinguishable from a guess.
- Rated flow is the manufacturer's open-flow figure, measured with no media and no head height.
- Losses combine multiplicatively rather than by addition.
- Default loss fractions are AquariumHQ editorial estimates from typical installations, not measurements of any specific product.
Limitations
Where this calculation stops being reliable. Read these before acting on a result.
- Turnover is an average and says nothing about distribution. A tank can have good turnover and still have dead corners.
- The right turnover depends on the animals: 2–3× for still-water species, 10× or more for hillstream fish.
- Loss fractions vary widely between products and installations. Measure by timing a bucket fill if it matters.