Aquarium filter flow & turnover calculator

Find the filter flow your tank needs, how many times an hour your filter turns the water over, and how much extra circulation a reef needs.

Inputs

From the box or manual. Optional: add it to see how your filter measures up.

Recommended filter flow

220GPH

Range 165–220 GPH

4× per hour for 55 gal.

Target turnover
4× per hour
Acceptable range
165–220 GPH
Your filter
Not entered
Recommended flow against the target range
220GPH

For 55 gal (freshwater community), aim for 220 GPH, anywhere from 165 to 220 GPH. The gauge marks the target range in green and the under-powered zone in amber.

How it works

Turnover rate is how many times an hour your filter moves a tank’s worth of water. Multiply it by the tank volume to get the flow you need.

turnover (per hour) = filter flow (GPH) ÷ tank volume (gal)
recommended flow    = tank volume × target turnover
  • Freshwater community: 3–4 turnovers an hour. MarineAndReef puts filtration at 3–4 times an hour, and Aqueon’s canister ratings work out to about 2.6–4 times an hour at each filter’s largest tank size.
  • Heavy stocking or messy fish: 4–10 turnovers an hour. The top of the range is MarineAndReef’s figure for high-flow freshwater species.
  • Gentle fish such as bettas and fancy or long-finned fish: 2–3 turnovers an hour, so the current doesn’t push them around.
  • Reef tanks: the filter still runs at 3–4 turnovers an hour. The corals get additional circulation on top: 20× for soft and large-polyp corals, 30× for mixed reef, 40–60× for small-polyp stony corals.
  • The gauge shows your filter’s rated flow against the target range (green). If you leave the filter blank, it shows the recommended flow instead.

Worked example

A 75 gallon freshwater community tank with a 300 gph filter:

  • Target: 75 × 3 to 75 × 4 = 225 to 300 GPH
  • Turnover: 300 ÷ 75 = 4 times an hour, at the top of the range. Aqueon rates the 300G for up to 75 gallons.

For a 100 gallon mixed reef, filtration needs 300–400 GPH. Total circulation, with powerheads, is 30 × 100 = 3,000 GPH.

Tips from the fish room

  • Watch the fish, not just the number. If your fish hover in the outflow or fight the current, turn it down or add a baffle.
  • Don’t count the powerheads as filtration. They move water inside the tank but don’t pass it through media.
  • Clean the filter on a schedule. Clogged media cuts flow without anything looking wrong.
  • Match the flow to the tank shape. A long, shallow tank needs outlets at both ends; one filter at one end leaves dead spots.

FAQ

What GPH filter do I need for a 55 gallon tank?

For a freshwater community tank, aim for about 165–220 GPH, which is 3–4 turnovers an hour. Aqueon's 200 gph canister is rated for up to 55 gallons, right in that range. A heavily stocked tank can use more, up to several times that.

What is turnover rate?

How many times an hour the filter moves a volume of water equal to your tank. A 55 gallon tank with a 220 GPH filter has a turnover rate of 4 times an hour.

Can a filter be too strong?

For most fish, no. More flow through a filter means more cleaning, with diminishing returns. The limit is the current in the tank. Bettas, fancy goldfish and other long-finned fish struggle in strong flow, so aim low and baffle the outlet.

Does a reef tank need a bigger filter?

Not for filtration, which is the same 3–4 turnovers an hour. The corals need extra circulation, from powerheads or wavemakers, about 20 times an hour for soft and large-polyp corals, 30 for a mixed reef, and 40–60 for small-polyp stony corals.

Is rated GPH what my filter really moves?

Rarely. The rating is for a clean filter with no media, no plumbing and no lift. Expect noticeably less in a running tank, and less again as the media clogs, which is why this page's range starts below the target.

Sources

  1. Tank Turnover: How Much Do You Need and How To Get It, MarineAndReef.com. Filtration 3–4 times per hour; reef circulation 20× for soft and large-polyp corals, 30× for mixed reef, 40–60× for small-polyp stony corals; 10× for high-flow freshwater species.
  2. QuietFlow Canister Filters Instructions (200G, 300G, 400G), Aqueon. 200 gph for up to 55 gal, 300 gph for up to 75 gal, 400 gph for up to 155 gal.

Formula and sources last checked September 30, 2026. How we test formulas.

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