Aquarium filters
Choose an aquarium filter based on how much flow your animals can handle and how much waste they make, aiming for a flow rate of about 4 to 10 times the tank volume per hour. Bettas, shrimp and axolotls do best with gentle sponge filters, while goldfish and turtles need large-capacity filters such as canisters or oversized hang-on-back filters.
Which filter does what
- Sponge FilterGentle safe biological filtrationBest for sensitive or low-flow inhabitants including bettas, shrimp, axolotls, and fry tanks.Amazon ↗
- Hang-On-Back (HOB) FilterEasy customizable multi-stage filtrationIdeal for standard freshwater community tanks needing convenient maintenance and flexible media options.Amazon ↗
- Canister FilterHigh capacity external power filterA strong choice for medium-to-large tanks with heavy waste producers like goldfish, large cichlids and aquatic turtles.Amazon ↗
- Internal FilterCompact fully submerged circulationUseful for small nano tanks, quarantine setups, or supplementing flow in targeted dead spots.Amazon ↗
Sizing: Size community tank filters to turn over the tank volume about 4 to 10 times per hour (for example, 80 to 200 GPH for a 20-gallon tank). For messy animals like aquatic turtles or goldfish, buy a filter rated for 2 to 3 times your actual water volume.
What each animal's guide calls for
From the checklists on each care guide, so this table and those pages always agree.
- Betta fishSponge filter and air pump5 gal min$12–$20
- Red-eared sliderCanister Water Filter100 gal min$120–$250
- AxolotlSponge Filter or Low-Flow Filter29 gal min$12–$30
- GoldfishCanister Filter (rated 2x tank volume)40 gal min$70–$160
- Freshwater shrimpAir-Driven Sponge Filter5 gal min$8–$15
- Neon tetraHang-On-Back or Sponge Filter20 gal min$15–$35
- GuppySponge Filter or Low-Flow HOB Filter10 gal min$10–$25
- Mystery snailSponge Filter with Air Pump5 gal min$10–$20
- AngelfishHang-On-Back Power Filter29 gal min$25–$50
- Musk turtleCanister Aquarium Filter40 gal min$80–$180
- Bristlenose plecoPower Filter or Canister Filter20 gal min$25–$50
- African dwarf frogSponge Filter and Air Pump10 gal min$12–$22
How to choose
- 01Identify the bioload and flow tolerance of your aquatic animalsBettas, dwarf shrimp and axolotls need gentle flow, while turtles and goldfish need lots of biological media and strong circulation.
- 02Calculate required flow rate in gallons per hour (GPH)Aim for about 4 to 6 times the tank volume per hour for general community tanks, and 8 to 10 times for heavy-waste setups.
- 03Prioritize reusable biological media over disposable cartridgesSponges and porous ceramic media hold the beneficial bacteria that break down ammonia and nitrite, and they can be rinsed and reused for years.
- 04Measure physical clearance around and inside your tank cabinetCanister filters require vertical cabinet space below the aquarium, HOB filters need clearance behind the glass, and internal filters consume interior swimming space.
- 05Select a filter with adjustable flow controls or spray barsFlow adjustment lets you fine-tune water velocity if currents prove too strong for long-finned fish or surface-dwelling species.
Common mistakes
- Replacing all filter media at once, which destroys the established nitrifying bacteria colony and causes lethal ammonia spikes.
- Rinsing dirty bio-media or sponges under untreated tap water, where chlorine can kill beneficial bacteria.
- Throwing out reusable sponges every few weeks because the box says to, instead of squeezing them out in old tank water.
- Putting bettas, shrimp or axolotls on strong filter outflow without a spray bar, baffle or sponge to soften it.
- Under-filtering turtle or goldfish setups by relying on standard fish tank ratings rather than actual waste output.
Questions people ask
What is the difference between mechanical and biological filter media?
Mechanical media (sponges and filter floss) traps floating waste and debris. Biological media (ceramic rings and coarse sponge) gives beneficial bacteria a place to grow, and they turn toxic ammonia into nitrite and then into much less harmful nitrate.
How do I safely clean my aquarium filter media?
Squeeze out sponges and swish bio-media in a bucket of old tank water during a regular water change. Avoid hot water or untreated tap water, which can kill the bacteria.
How often should aquarium filter media be replaced?
Ceramic media and coarse sponges last for years and only need replacing when they fall apart. Filter floss and carbon need changing more often. Never replace more than about half of the biological media at once.
What filter is recommended for bettas, dwarf shrimp, and axolotls?
Air-driven sponge filters are the top choice because they filter and add oxygen without blowing fragile animals around. If you use a hang-on-back filter, cover the intake with a pre-filter sponge so fins, limbs and baby shrimp don't get sucked in.
How much filtration capacity do goldfish and aquatic turtles need?
Goldfish and turtles make a lot of waste, so aim for 8 to 10 times the tank volume per hour. Many keepers choose a filter rated for 2 to 3 times the actual tank volume.