Aquarium Filters & Pumps: Choosing the Right One
Match the filter style to your tank and fish.
| Tank and fish | Filter style | Why |
|---|---|---|
| Nano tank, betta or shrimp | Sponge or small internal | Gentle flow; tiny animals aren't sucked in |
| Community tank, 10–30 gallons (38–114 liters) | Hang-on-back | Simple to service, plenty of capacity |
| 55 gallons (208 liters) and up, or heavily planted | Canister | Most media, handles a heavier load |
| Goldfish or large cichlids | Canister or an oversized hang-on-back | Lots of waste needs extra margin |
| Fry or breeding tank | Sponge | No strong intake to pull in babies |
A filter runs around the clock, catching debris and housing the bacteria that break down fish waste. Two things matter most: matching its rating to the tank, and treating media as an ongoing supply, not a one-off purchase.
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Hang-On-Back Filters
A hang-on-back filter clips over the back rim, draws water up an intake tube, runs it through media and spills it back in. It is the style in most beginner kits: quick to install, easy to service, and the little waterfall helps add oxygen at the surface.
Canister Filters
A canister sits in the cabinet below the tank, sealed, pulling water through stacked trays of media and returning it through a spray bar. It holds far more media than a hang-on-back of the same size, which suits big, planted or heavily stocked tanks. Check hose connections after every clean so it can't leak.
Sponge and Internal Filters
A sponge filter is just an air pump, airline tubing and a foam block, which makes it the gentlest choice for fry, shrimp and bettas. The foam becomes packed with good bacteria, so many keepers run one as a backup alongside the main filter. An internal filter sits under the water on suction cups, which suits small or rimless tanks.
Air Pumps and Powerheads
An air pump drives a sponge filter or an air stone, and surface movement from the bubbles helps oxygen exchange. A powerhead pushes water to create current for fish from flowing rivers, or to clear dead spots where debris settles. Fit a check valve in the airline so water can't siphon back into the pump.
Matching the Filter to the Tank
A filter's rating should at least match the tank's volume, and going up a size covers the flow lost to decor, plants and clogging media. Messy fish such as goldfish and larger cichlids need more filtration than a few small tetras in the same tank; see African cichlids and goldfish tanks.
Too much current can tire bettas, long-finned fish and fry. A spray bar or flow-reducing attachment lets a strong filter run gently.
Filter Media Basics
- Mechanical (floss, sponge pads) traps debris and needs rinsing most often.
- Biological (ceramic rings, the sponge itself) houses the bacteria that break down ammonia and nitrite. Leave it in place as long as it holds together.
- Chemical (usually activated carbon) removes some dissolved substances and odors. It is optional for most tanks.
If you ever need to treat sick fish, see your vet or a pet or aquatics store with trained staff first. Carbon can remove some treatments from the water, so ask whether to take it out.
Replacement Media
Rinse sponges and bio media in old tank water from a water change, never under the tap, because chlorine kills the bacteria. Clean or replace only part of the media at a time. Replacing everything at once can wipe out the bacteria and restart the cycle, with an ammonia spike within days.
Frequently Asked Questions
What filter shoppers ask most.
Hang-on-back or canister?
A hang-on-back is simpler and suits most community tanks. A canister holds far more media and suits large, planted or heavily stocked tanks. Tank size and how much waste your fish make usually decide it.
Is a bigger filter always better?
For capacity, usually yes, but strong current can tire bettas, long-finned fish and fry. A spray bar or flow reducer fixes that without downsizing.
Can I run two filters on one tank?
Yes. Many keepers add a sponge filter to the main filter for extra bacteria and a backup if one fails.
How often should I clean the media?
Rinse mechanical media in old tank water every few weeks, or when flow drops. Leave biological media alone as long as possible, and never clean everything on the same day.
Do I need carbon?
Most tanks don't. Mechanical and biological media do the essential work.
What happens if I replace all the media at once?
You remove most of the bacteria and can restart the cycle, with an ammonia spike within days. Stagger changes, one type at a time.
Related Reading
- Cycling a tank: how the filter bacteria get started.
- Aquariums and stands: choosing the tank.
- Cloudy water fixes: when the filter can't keep up.
If fish seem unwell, check that the filter is running and test the water before anything else, then ask a vet who treats fish or trained aquatics staff.