Use turnover as one comparison metric rather than treating it as proof of filtration quality.
Divide filter flow in litres per hour by aquarium water volume to get turnovers per hour. Or multiply a chosen turnover target by volume to get a comparison L/h.
Fish tolerance for current, plant density, waste production, filter type and overall circulation can change what is useful. There is no universally correct multiplier.
Original diagram supporting the choosing a filter-turnover target explanation.
Media resistance, dirty sponges, hoses, bends and head height can lower real flow compared with a pump’s box rating.
A mature biological filter and stable water quality cannot be inferred from litres per hour. Testing and filter maturity remain essential.
Look for dead spots, animal stress, stable water quality and actual filter maintenance performance rather than relying only on the headline number.
Tank volume is the water being circulated. Rated flow is the pump or filter specification under stated conditions. Turnover is flow divided by tank volume. Confusing those numbers is why raw L/h figures are hard to compare between aquariums of different sizes.
The right current and filtration strategy depends on the animals, planting, waste load and equipment layout. Use a turnover target as a planning input, not as a universal welfare standard.