Review: Hydroset thermostat from Hydor


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Nathan Hill gets to test this new external thermostat, which is available with or without a digital display depending on your budget.

It’s good

It’s better than good, it’s outstanding. Usually, if I want an external thermostat (and I often do) I need to sniff about in a reptile supplier’s premises. As we’ve all become increasingly used to heaters with thermostats combined, so the market for separate thermostats has declined, but as far as I’m concerned they still have an essential role to play.

For this review I used the Hydroset with a Dennerle heater cable to one of PFK's step-by-step projects up to temperature, and it behaved admirably.

The digital screen gives you two readouts: the intended temperature you want to achieve, which you can simply set with a rotating dial, and the actual measured temperature in the tank.

The settings move at 1°C increments, anywhere as high as 35°C/95°F and as low as 6°C/43°F. Though mine was used with a cable, now that the project is over, I’ve attached this ‘stat to a standard 100w heater running in another tank for extra security. Even if my heater fails and tries to go ballistic, the thermostat will cut it out way before I get overheating fish.

The device is small, about half the size of a plump apple, and rendered in smart black and burgundy. With the pre-cut holes in both top and bottom, a discretely positioned screw or hook will let you hang it up wherever is convenient or smart.

Accuracy is astounding when cross-referenced with my many digital and glass thermometers, and the thermostat never lets water get as much as a degree above the specified requirement. In my case, I didn’t notice it drop 1°C under while it was running, either.

Reviewed here is the digital display model, but for those on a budget, there’s also a non-digi version, with settings directly on the controlling dial, for around half the price of the digi model.


As is the case for most good hardware, it’s expensive and unless you have unusual heating requirements, such as undergravel cables, or even under-tank heater mats, it might be a little too ostentatious to justify for use on the everyday home aquarium heaterstat.

Because of the nature of using heater cables, the Hydroset has three wires leading into it: one from the mains, one with a socket for your heater and one for the thermometer. If you’re not careful when setting up, you’ll soon have a tangled octopus of a thing beneath your set-up.

Though the thermometer cable has two suckers and hoops to hold it in place, it’s still an extra worry to ensure that it’s always submerged in the tank. If it comes loose and starts to read a cold room instead of a hot tank, it’ll crank that heater on and keep it there. But this is the nature of the beast with all external ‘stats. Keep that dial away from roaming child hands too.

The verdict

I love it to bits. The thermostat does everything it is meant to, and when I put it through its paces, it behaved impeccably. I’ll be keeping it safe and will consider it a standard feature on all future set-ups.


  • Able to utilise novel heaters such as cables for smaller tanks.
  • Accurate to just 1°C.
  • Smart looking for minimalist aquarists.
  • Extra safety if using unreliable heaterstats.


  • Lots of cables involved.
  • Risk of thermometer coming loose from tank.
  • Expensive if just used as a failsafe.

Price: Digital display Hydroset, £62.79; non-display Hydroset £33.69. More info:

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