
How Many Fish Can I Put in My Tank? Honest Stocking Guide
The inch-per-gallon rule has killed more fish than any other piece of aquarium advice. Here's what to use instead.
8 min read
Under 40 dB, which is quieter than the room.
Under forty decibels is quieter than a normal conversation, which matters because an aquarium air pump runs continuously and most of them end up in a room somebody sleeps in.
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Size: Single outlet
Why you'll love it
A buzzing pump on a shelf gets switched off at bedtime and forgotten by morning. Under 40 dB with rubber feet is the difference between a pump that runs and one that sits in a drawer.
The four-outlet model can run two sponge filters, an air stone and an ornament at once, each dialled separately. Splitting one un-valved outlet just starves whichever line is furthest away.
We checked the electrical spec on every pump in this range and most were 110 V or unstated. This one is explicitly 220–240 V at 50 Hz, which is what a UK socket delivers.
Good fit if
Look elsewhere if
Oxygen enters water at the surface, where it meets air. Bubbles rising through the water column exchange very little gas on the way up; what they do is disturb the surface when they break, and that agitation is where the exchange actually happens. So a pump is oxygenating the tank indirectly.
It also drives air-powered sponge filters, which need nothing but rising bubbles to pull water through a sponge. That makes them the right filtration for fry, shrimp and betta tanks, where an impeller would injure small animals and the current from a powered filter is more than the fish want.
Most air pump noise is not the pump; it is vibration transmitted into whatever it is standing on. A pump on a glass cabinet or a hollow shelf turns that surface into a soundboard, and the same unit on a folded towel is often barely audible. Multi-stage internal damping addresses the rest.
A rattle that has developed over time usually means the diaphragm is tiring or the unit has worked itself against a wall. Check the standing surface first before assuming the pump is failing, since it is the cheapest thing to fix and it is the cause more often than not.
Choose the outlet count on how many air-driven devices you have rather than on tank size. One outlet suits a single sponge filter or air stone; two covers a filter and a decorative bubble bar; four is for running several tanks from one unit, which is common in a fish room.
Individual flow valves matter because they let you turn one line down without throttling the pump itself. Restricting the pump to reduce bubbles makes it work against back pressure, which shortens its life. Bleeding the excess off with a valve is the correct way to do it.
In the box
How it works
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The details
| Version | Outlets | Best for |
|---|---|---|
| Single | 1 | One sponge filter or air stone in a single tank |
| Double | 2 | A filter plus a bubble bar, or two small tanks |
| Four | 4 | Several tanks, or a fry and quarantine setup |
Choose on the number of air-driven devices, not on tank volume. Unused outlets should be capped or valved shut so pressure is not lost through them.
Good questions
The pump is rated 220–240 V at 50 Hz, which is correct for UK mains. We are confirming the fitted plug type with the supplier. If a two-pin European plug is supplied you will need a standard travel adapter, and we will say so on this page once confirmed.
One outlet per air-driven device. A single sponge filter needs one; a sponge filter plus an air stone needs two. Buy one size up if you expect to add a second tank.
Yes, and it is worth the pound it costs. If the pump sits below the water line and the power goes off, water siphons back down the airline into the pump without one.
It is specified at 220–240 V, 50 Hz, which is UK mains. Check the plug type on arrival and use a proper adapter rather than anything improvised if one is needed.
One per air-driven device. A single sponge filter needs one outlet; a filter and a bubble bar need two. Cap or valve off anything unused.
If the pump sits below the water line, yes. Without one, a power cut lets water siphon back down the airline into the pump and ruin it.
Last reviewed 30 August 2026
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