Calculate nominal hourly turnover from filter flow and working water volume, and calculate the delivered flow needed for a turnover you choose. Use litres for volume and litres per hour for flow throughout.
For measured delivered flow, leave derating at 0%: the measurement already includes losses in the installed setup. Enter a positive derating only to model an additional percentage reduction or to estimate delivered flow from a stated baseline. The calculator does not select a stocking-based target; the example target is an arithmetic illustration, not a recommendation.
Use the actual water volume represented by your calculation, rather than the aquarium’s advertised capacity. Keep the same volume boundary when comparing results; if you include sump water, include it consistently.
Enter flow through the filter in L/h. Do not include a circulation pump that bypasses the filter. For measured installed flow, use 0% derating unless deliberately exploring a further reduction. For a baseline rating, any derating is your explicit assumption, not a loss predicted by this tool.
Both calculation directions appear together. The entered baseline flow determines the current turnover result. Your selected turnover determines the required-flow results independently of that baseline flow.
All volume, flow and turnover entries are numeric magnitudes in the units printed in their labels. Use L, L/h and per hour exactly as shown; this calculator does not convert gallons or minutes.
The ANGFA Home of the Rainbowfish discussion of filter turnover gives nominal turnover time as water volume divided by pumping rate. Taking the reciprocal with flow expressed per hour gives nominal hourly turnover, T = Q/V. Rearranging gives Q = TV.
The derating expressions are percentage arithmetic: a reduction of d% retains 1 − d/100 of the baseline. They are a user-selected scenario model, not an empirical pump-performance formula. Nominal turnover measures an equivalent volume pumped; it does not establish that every portion of the aquarium water has passed through the filter.
| Scenario | Inputs | Calculation | Result |
|---|---|---|---|
| Measured delivered flow | 100 L; measured flow 500 L/h; reduction 0% | 500 ÷ 100 | 5 turnovers per hour |
| Assumed reduction from a baseline | 100 L; baseline 500 L/h; reduction 20% | 500 × 0.80 = 400 L/h; 400 ÷ 100 | 400 L/h delivered; 4 turnovers per hour |
| Flow required for a selected target | 100 L; selected turnover 5 per hour; reduction 20% | 5 × 100 = 500 L/h; 500 ÷ 0.80 | 500 L/h delivered required; 625 L/h baseline required |
| Zero measured flow | 100 L; measured flow 0 L/h; reduction 0% | 0 ÷ 100 | 0 turnovers per hour |
Accepted inputs are working volume 0.1–1,000,000 L, baseline flow 0–10,000,000 L/h, reduction 0–99.9%, and selected turnover 0–1,000 per hour, with input increments of 0.1. These are computational bounds, not recommended operating ranges. A zero target is permitted for arithmetic completeness and produces zero required flow.
Volume must be positive. A 100% reduction is excluded because no finite baseline flow can deliver a positive target after complete flow loss. If the runtime reports a result as unavailable, do not interpret it as zero; check the inputs. Displayed results are rounded.
This calculation does not establish biological filtration capacity, livestock suitability, oxygenation or the distribution of current within the aquarium. It does not prescribe a universal turnover target. The required baseline result is conditional on your chosen percentage, not a guarantee that a particular filter will achieve the target.