Filter Flow Rate Calculator
Check whether your filter turns over the tank enough times per hour.
How it works
Turnover (×/hr) = Filter flow rate (L/h) ÷ Tank water volume (L). Aim for 4× for low-stock/planted tanks, 6-10× for community tanks, and 10×+ for messy or heavily stocked tanks. Account for media reducing rated flow by ~30%.
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Formula & Method
Turnover (×/hr) = Filter flow rate (L/h) ÷ Tank water volume (L). Aim for 4× for low-stock/planted tanks, 6-10× for community tanks, and 10×+ for messy or heavily stocked tanks. Account for media reducing rated flow by ~30%.
Example Calculation
A 200 L tank with a 1000 L/h canister = 1000 ÷ 200 = 5× turnover. After media losses (~700 L/h effective) it's ~3.5×, so you may want a larger filter.
Frequently Asked Questions
How much filter flow does my aquarium need?
Four to six times the tank volume per hour for planted and community tanks, six to eight for heavily stocked freshwater, and eight to ten for marine fish-only systems. Reef tanks need far more total water movement, but from powerheads rather than the filter.
Is my filter's rated flow accurate?
No. Ratings are measured with an empty filter and no hoses. Real flow with media installed is typically 30-50% lower, and drops further as media clogs. Multiply the rating by about 0.6 for a working estimate.
Can a filter be too strong?
Yes. Bettas, gouramis, long-finned fish and blackwater species are stressed by strong current and will hide rather than adapt. Use a spray bar, a wider outlet or a flow valve to reduce it.
Should I run two smaller filters or one large one?
Two smaller filters give redundancy, spread flow more evenly and let you clean one at a time without losing the whole bacterial colony. On tanks over 200 litres this is generally the better approach.