Do You Really Need an Air Pump?

Written 2026-10-30

Whether you need an air pump mostly comes down to how much your filter already stirs the surface. Running the Water Kiwoogi simulator on a 90cm tank with only a low-agitation canister filter (agitation 0.5) and the heater at 27°C, we stocked 16 stream-loving panda garra and 10 hardy guppies on day 30 and watched for 90 days. Only the panda garra died — one on day 52, another on day 70 — while all 10 guppies made it through untouched. Adding one small air pump (surface agitation +0.8) to the same tank let all 26 fish survive, and so did swapping to a filter that already agitates the surface a lot on its own, a large hang-on-back filter (agitation 1.7), with no air pump at all. So if your filter is already stirring the surface hard, you probably don’t need a pump — but a low-agitation filter (canister, undergravel) paired with warm water and an oxygen-hungry species is exactly where one small air pump can decide who survives.

Filters disturb the surface by very different amounts

Every filter in Water Kiwoogi carries its own surface-agitation number. The higher it is, the more oxygen dissolves — but the faster CO₂ escapes too. An air pump simply adds its own number on top.

A small air pump adds +0.8, a large one +1.6, stacking directly on top of whatever your filter already gives. If you’re running a low-number filter like a canister or undergravel, one small pump can nearly double your total agitation.

What we actually ran — only the stream-loving species struggled

We set up a standard 90cm tank with only a mid-size canister filter (the lowest surface agitation on the list), no air pump, and the heater held at 27°C. After letting it fully cycle, we stocked 16 panda garra together with 10 guppies on day 30 and watched for 90 days. Panda garra live in fast, oxygen-rich streams and carry the lowest oxygen tolerance in this catalog (0.7, versus the default 1.0); guppies sit at the opposite end (1.2, the most oxygen-tolerant).

The low-oxygen threshold works out to the base threshold (4.0mg/L) times (2 − tolerance). That puts panda garra at 5.2mg/L and guppies at 3.2mg/L. At 27°C, water can only hold up to 7.87mg/L of oxygen to begin with, and with only a weak-agitation filter running, oxygen in this tank bottomed out at 4.46mg/L — below the panda garra’s threshold but nowhere near the guppy’s, exactly the band that only catches the sensitive species. Panda garra died one at a time on day 52 and day 70, leaving 14, while all 10 guppies made it through the full 90 days. Ammonia and nitrite never came close to a dangerous level the whole time (nitrite peaked at just 0.2ppm on a test-kit scale) — the water itself was stable, and every death in the log was logged as low oxygen.

One air pump, or a filter that already agitates enough

We changed exactly one thing in the same tank — added an air pump, raising total surface agitation from 0.5 to 1.3. All 26 fish, panda garra and guppies alike, survived the full 90 days with zero low-oxygen deaths. Skipping the air pump entirely but swapping in a large hang-on-back filter (agitation 1.7) on its own gave the exact same result — 26 of 26 survived. Both routes work the same way, by speeding up how fast the surface trades gas with the air, so if your filter is already doing that job, there’s little reason to add a pump on top.

Planted tanks running injected CO₂ usually skip the air pump on purpose. The more you agitate the surface, the faster CO₂ escapes with it — the catalog’s own note on the large hang-on-back filter says outright that it’s “the worst possible match for a CO₂-injected planted tank.” That’s why CO₂ tanks tend to run a low-agitation filter like a canister instead, and leave oxygen to plant photosynthesis and slow surface exchange rather than a pump.

So an air pump tends to matter when: ① you’re running a low-agitation filter (canister, undergravel) and nothing else is stirring the surface, ② the heater sits near the top of a species’ comfortable range (which lowers the oxygen ceiling), and ③ you keep an oxygen-hungry species like panda garra. If instead you already run a high-agitation filter (large hang-on-back, overhead) or inject CO₂, an air pump is often unnecessary — or even counterproductive.

The button below is the tank from this guide with the small air pump added, where all 26 fish survived.

The numbers in this guide come from the Water Kiwoogi simulator model; real tanks can differ.