The best heater for a 5 gallon tank

Adjustability is worth more on a 5 gallon tank than on any other size, because a small volume responds fast to a thermostat that is set wrong. A dial lets you set 78 F and verify it, rather than trusting a factory setting you cannot change.

10 W per gallon sounds like a lot, and on a big tank it would be. On 5 gallons it is the practical floor, because 25 W heaters — the figure the arithmetic actually asks for in a normal room — are barely made any more.

Fluval computer-calibrates the thermostat and publishes a temperature range. What it does not publish, in the way Eheim does for the Jager, is a control-accuracy tolerance, so we do not state one.

The honest costs. It is the most expensive heater here. It is a glass-bodied unit, so it breaks if you knock it against the rim or leave it exposed while draining the tank. And check the length against your tank's height before you buy: a 5 gallon tank is short, and a long heater has to lie at an angle.

The value pick, and the one most likely to be bought without thinking about it, because it is cheap and because the listing names the exact tank sizes this page is about.

It is preset. There is no dial: it holds whatever temperature Tetra chose, and your job is to confirm that number with a thermometer rather than to select it. In an ordinary heated room holding a community tank that is usually fine, and it is genuinely one less thing for a first-timer to set wrong.

It becomes the wrong heater in two cases: a cold room, where a preset with no headroom cannot hold the lift, and a species with a specific temperature requirement that does not match the preset.

The honest costs. No temperature selection at all. Tetra's own site does not respond to us, so we cannot print an accuracy tolerance or a preset figure we have verified. And like every heater here, no thermometer is included — which on a preset unit matters more, not less.

The appeal is the controller: a readout and buttons outside the tank, so setting and checking the temperature does not mean fishing a dial out of the water and squinting at it through algae.

On a nano tank that convenience is not trivial. The heaters in this size class are small, the dials are small, and the most common reason a beginner never adjusts a heater is that adjusting it is fiddly.

The honest costs. A digital readout on a controller is not a thermometer in the water — it reports what the controller believes, and the whole point of an independent thermometer is that it does not. hygger publishes no control-accuracy tolerance we can verify. And the controller is one more component to place, keep dry, and eventually replace.

Read that computed line carefully, because it is the most useful thing on this page: the same 50 W heater is marginal on a 20 gallon tank and generous on a 5. Wattage is not a property of the heater, it is a relationship between the heater, the volume and the room.

On a 5 gallon tank in a cold room — a conservatory, a garage office, a bedroom with the heating off overnight — this is the pick, because the headroom is there when the lift gets large.

The honest costs. Its stated 20 gallon ceiling is the kind of number that gets people into trouble on a bigger tank; here we are using it well inside its range. No published accuracy tolerance we can verify. Glass bodied, so treat it carefully during water changes.

On a 5 gallon tank a stuck-on heater can add several degrees in an hour, because there is so little water to absorb the heat. That is the failure mode this size is prone to, and a thermometer is the only thing that catches it.

A heater dial is a setting. A thermometer is a reading. On a tank this small, the gap between them can be lethal inside a single day.

The honest costs. It is one more thing in a small tank, and a stick-on strip type reads the glass rather than the water — put an in-tank thermometer in instead, and put it at the opposite end from the heater.

The skip entry exists because the instinct to oversize is strong and on this tank size it is dangerous rather than merely wasteful.

A 100 W heater on a 5 gallon tank is 20 W per gallon. If the thermostat sticks on — the normal way heaters fail — the temperature rise is fast and there is no thermal mass to slow it down. The same failure on a 20 gallon tank gives you hours to notice; here it gives you less.

It is a good heater. It is the right heater for a 20 gallon tank, and it is on our main heater shortlist for exactly that. On 5 gallons, buy the 50 W version of the same line instead.