Free tool — no sign-up, no email needed. It gives a starting range, not a guarantee. Fish species, tank shape, media, tubing and maintenance all change real flow. Check the product listing before you buy. This page contains Amazon affiliate links — see our affiliate disclosure.

Aquarium Filter Finder + GPH Calculator

Short answer: Enter your tank size, stocking level and fish type below, and this tool will tell you the GPH range your tank needs — and name a specific filter from our own shortlist that fits it. Most calculators stop at “you need a hang-on-back filter.” That does not help you buy anything. This one names the filter, its price range and why it fits, so you can check the price and buy with confidence.

If you already own a filter, skip to the second tool: enter your tank size and the filter's advertised GPH and it will tell you whether your turnover is in range, too low, or too strong for your fish.

Filter Finder: Answer 5 Questions, Get a Specific Pick

Already Have a Filter? Check Its GPH

Enter your tank size and the filter's advertised GPH. The tool tells you the turnover and whether it is in range for your setup.

Pump output is not always filter circulation. Fluval, for example, lists the 207 at 206 GPH pump output but 121 GPH filter circulation. Compare circulation to circulation, not one brand's pump figure to another brand's circulation figure. Media, tubing, water level and cleaning also reduce real flow.

How GPH Works — The Simple Version

GPH stands for gallons per hour: how much water your filter moves in one hour. Turnover is GPH divided by tank size. A 300 GPH filter on a 55-gallon tank gives about 5.5x turnover per hour (300 ÷ 55 = 5.5). That one number is the easiest way to judge any filter, whatever its type or brand.

For most community tanks, 4–6x turnover per hour is the sweet spot. Below 4x, waste can build up faster than the filter handles it, especially if you feed heavily. Above 6x, the current can stress fish that prefer calm water, and food gets blown around before fish can eat it. Bettas, shrimp and fry do best at a gentler 3–4x, while goldfish and cichlids — heavy waste producers — need 5–8x. This tool applies those rules automatically when you pick your fish type and stocking level.

One warning that saves beginners money: the headline GPH is usually measured with no media, no hoses and no height to climb. Once you add media, hoses and the height under your cabinet, real flow drops. That is why Fluval publishes two numbers for the 207 — 206 GPH pump output and 121 GPH circulation — and why this tool uses the circulation figure for the 207. When a brand only gives one number, assume real flow will be a little lower and give yourself headroom.

What Size Filter Do I Need? Quick Guide by Tank

Filter Types Explained in 30 Seconds Each

Hang-on-back (HOB): Hangs on the tank rim, easy to install and maintain, cheapest to start. Best for tanks up to about 70 gallons. Downside: less media space than a canister, and some models need cartridge refills.

Canister: Sits under the tank, holds the most media, runs quietest, keeps the tank looking clean. Best for 30 gallons and up, and for heavily stocked tanks. Downside: higher price and longer setup, and you must prime it before starting. See our full best canister filters guide.

Internal: Sits inside the tank, cheap and simple, good for small tanks and as a second filter. Downside: takes up space inside the tank and is not ideal for shrimp or fry unless the intake is covered.

Sponge: Air-driven, gentle flow, no cartridges, lasts for years with rinsing. Best for betta, shrimp and fry tanks, and as a backup filter. Downside: needs a separate air pump, and it does not polish water as finely as a canister.

Still deciding between types? Start with our best aquarium filtration guide, then come back here and run the Finder with your real tank size.

5 Mistakes This Calculator Helps You Avoid

1. Buying on headline GPH alone. Always check whether the number is pump output or circulation, and whether your tank is at the top of the filter's rated range. If it is, size up.

2. Ignoring stocking level. A lightly stocked 55-gallon tank and a heavily stocked 55-gallon goldfish tank do not need the same filter. That is why this tool asks about stocking — the answer changes the GPH range.

3. Too much flow for bettas and shrimp. More flow is not always better. Gentle-flow fish need 3–4x turnover and a protected intake, or they will hide, stop eating, or get pulled toward the filter.

4. Forgetting the hidden costs. Cartridge filters need refills, sponge filters need an air pump, and canister filters need media replacements over time. The cheapest filter on day one is not always the cheapest over a year.

5. Skipping maintenance. Even the right filter fails if it is never cleaned. Clean mechanical media every 4–8 weeks, rinse it in tank water (never tap water, which kills beneficial bacteria), and check seals and impellers. A clean filter keeps its flow; a clogged one does not.

More Aquarium Filter Guides

Best Fish Tank Filters 2026 · Best Canister Filters · Best Aquarium Filtration · Good Aquarium Filter Guide · Best Rated Aquarium Filter · Freshwater Aquarium Filtration

Filter Finder FAQs

1. How do I calculate GPH for my aquarium?

Multiply your tank size in gallons by 4 to 6 for a community tank. A 55-gallon tank needs roughly 220–330 GPH of real circulation. For bettas or shrimp, multiply by 3 to 4 instead; for goldfish or cichlids, multiply by 5 to 8. Or use the calculator above — it does this math and names a filter for you.

2. Is 4x turnover enough for a fish tank?

For a lightly stocked community tank, yes — 4x is the low end of the normal range. For a normally stocked tank, aim for 4–6x. For heavy stocking or messy fish, 4x is usually not enough, and you should aim higher or choose a filter with more media capacity.

3. What GPH do I need for a 55-gallon tank?

For a 55-gallon community tank, aim for about 220–330 GPH. A filter rated around 300 GPH, such as a large HOB, or a canister like the VEVOR 224.5 GPH (rated 35–55 gallons) will be in range — always check the circulation figure, not just the pump figure, before you buy.

4. Can a filter be too strong for fish?

Yes. Too much current stresses bettas, shrimp, fry and other gentle-flow fish, and can blow food away before they eat it. If your turnover is above 6x for a community tank, or above 4x for bettas and shrimp, use adjustable flow, a spray bar, or a pre-filter sponge — or choose a gentler filter.

5. What is the difference between pump output and filter circulation?

Pump output is the flow with no media, hoses or height to climb. Filter circulation is the flow after media and plumbing — the number that actually matters in your tank. Fluval publishes both for the 207: 206 GPH pump output, 121 GPH circulation. When only one number is given, assume real flow will be lower.

6. Do I need a canister filter or is a HOB enough?

For tanks up to about 30 gallons, a good HOB is usually enough. For 30 gallons and up, especially heavily stocked tanks, a canister holds more media, runs quieter and keeps the tank cleaner. Compare both in our best fish tank filters guide before deciding.