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Choosing an aquarium filter

The right filter depends on your tank volume, fish load, and whether you want a simple setup or a planted/specialist system. This page explains the practical differences — not brand comparisons.

The core rule: turnover rate

A filter should turn over the full tank volume 4–10 times per hour depending on fish load. For a lightly stocked 60L community tank, aim for a filter rated at 240–360L/h. For messy fish (goldfish, large cichlids, plecos), push toward 8–10× turnover.

Tank sizeLight stockingHeavy stocking
30L120–180 L/h240–300 L/h
60L240–360 L/h480–600 L/h
100L400–600 L/h800–1000 L/h
200L800–1200 L/h1600–2000 L/h

These are starting ranges — reduce flow for slow-water species (bettas, discus, leaf fish).

Visual: flow midpoints by tank

Bars use the midpoint of each light / heavy band — same data model as the table above.

Hang-on-back (HOB)

Good all-rounder for 20–200L tanks. Easy media access and good mechanical filtration. Splash may add O₂. Not ideal for low-flow species or tanks without a lid.

Best for: Community tanks, beginners.

Canister filter

Large media volume, quiet, hidden below tank. Excellent biological filtration. More expensive and harder to clean than HOB, but better for heavily stocked or planted tanks.

Best for: 100L+, heavily stocked, planted tanks.

Sponge filter

Cheap, shrimp-safe, and gentle. Run on air or a small powerhead. Ideal for fry tanks, shrimp tanks, and bare-bottom setups. Not suitable as primary filtration for heavy bioload.

Best for: Shrimp, fry, nano tanks.

Internal filter

Submersible, compact, low cost. Suitable for small tanks and quarantine setups. Limited media capacity means it is best for light loads only.

Best for: <40L, quarantine, backup.

Common filter mistakes

  • Under-filtering for the actual load. The fish in your tank when full-grown — not the juveniles in the shop — determine bioload.
  • Over-filtration for slow-water species. Bettas, discus, and pea puffers do not thrive in strong flow. Reduce output or use a spray bar to diffuse it.
  • Replacing all media at once. Filter media holds the beneficial bacteria that cycle ammonia. Replace in stages over several weeks.
  • Cleaning media in tap water. Chlorine kills the bacterial colony. Rinse in old tank water only.
  • Never cleaning the impeller. A blocked impeller reduces flow silently. Check it when doing filter maintenance.

Plan with your fish in mind