Best Filter for a 20 Gallon Planted Tank

Why these three

A 20 gallon planted tank sits in the sweet spot for filter choices: small enough that a sponge filter still does the job for shrimp or a betta, large enough that a canister pays off if you want silence and flexible media.

Fluval 107 — the quiet option

The 107 is rated for 30 gallons but performs best on tanks at or below that rating. On a 20, it’s under-loaded, which means quieter operation, longer intervals between cleanings, and room to add media as your bioload grows. Priming is reliable; the taps are the common long-term failure point but easy to rebuild.

AquaClear 50 — the workhorse

An AC50 is the answer for 80% of 20 gallon planted tanks. The adjustable flow knob lets you throttle it down for a newly-planted setup, then open it up as plants fill in. The oversized media basket takes whatever you throw in. It’s louder than a canister and needs priming after a power loss — that’s it for the downsides.

Dual sponge — the shrimp-safe option

If your 20 is a shrimp tank, a filter with an open intake is a liability. A sponge filter (driven by an air pump) cannot shred babies, costs very little, and is trivial to maintain. Aesthetics take a hit — the sponge is visible in-tank — but for shrimp tanks this is the correct choice.

Sizing notes

A 20 gallon tall and a 20 gallon long behave differently. The long has more surface area per volume — better for plants, easier to oxygenate — and a single HOB usually suffices. The tall shape benefits from a filter that creates a full-column flow loop, which is where a canister with a spray bar edges out a standard HOB.