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Kindral

Digital Thermometer

The number your heater is not telling you.

The dial on a heater is a setting, not a reading. A separate thermometer is how you find out that a thermostat has drifted, and drift is what kills tanks quietly.

£8.99

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  • Probe reads the water, not the room
  • Display mounts outside the tank
  • Battery supplied, fitted
  • Range −50 to 110 °C
  • Black or white housing

Colour: Black

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Why you'll love it

Made for happy, healthy pets

A heater's dial is not a reading

Cheap heater thermostats drift, and the dial keeps saying what you set it to regardless. An independent thermometer is the only way to know what the water is actually doing.

You are looking for change, not accuracy

Rated at ±1 °C, so treat the absolute figure as approximate. What matters is that the same instrument reads the same each morning: a two-degree slide is the warning, whatever the true value.

The display stays dry

Stick-on strip thermometers fade and in-tank glass ones break. Probe in, display out means the electronics never sit in the water.

Good fit if

  • Any heated tank, which means most tropical setups
  • Spotting a heater that has stuck on before it cooks the tank
  • Acclimatising new fish, where matching temperature matters
  • Anyone relying on a heater's own dial

Look elsewhere if

  • You already run a controller with its own probe
  • You want something with an alarm, which this does not have
  • You need laboratory accuracy rather than practical accuracy

Why a heater dial is not a reading

A heater's dial tells you what it has been asked to do, not what the water is actually doing. Thermostats drift with age, and a heater set to twenty-five degrees can be holding twenty-two or twenty-eight after a year without anything looking wrong from the outside.

The failure that matters most is a thermostat sticking closed. The heater then runs continuously, and a small tank can climb several degrees in a few hours. It is one of the more common ways a tank is lost, and it is entirely preventable by looking at an independent reading once a day.

Stability over precision

Fish are far more sensitive to change than to any particular number within their range. A tank steady at twenty-four degrees is better than one averaging twenty-five while swinging two degrees either side, because it is the swing that stresses fish and suppresses their immune response.

That is why resolution to a tenth of a degree is useful even though the accuracy is about a degree. You are watching for movement rather than for an absolute figure: a reading that has changed by half a degree since yesterday tells you something even if the absolute number is slightly off.

Where to put the probe

Put the probe at the opposite end of the tank from the heater, at mid-depth. Next to the heater it reads the warm plume rather than the tank, and right at the surface it reads a layer that is cooler than the body of water. The far end at mid-depth gives the figure that matters.

Keep it out of the direct outflow of a filter for the same reason. The display mounts outside on the glass, which keeps the electronics away from the water entirely and means you can read it without opening the lid, and the probe can stay in permanently.

In the box

Everything you need

  • Digital thermometer with probe
  • Battery, fitted

How it works

Simple, from basket to doorstep

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The details

Specifications

Range
−50 to 110 °C
Accuracy
About ±1 °C
Display
LCD, 48 × 28.5 × 15 mm
Power
Button cell, included
Colours
Black or white

Probe and battery

Algae grows on the probe like anything else in the tank, and a thick coating slows its response. Wipe it during your weekly water change, and check the lead where it passes over the rim, since that is where a cable is pinched by a lid and eventually fails.

A button cell lasts a long time but it does die, and a dead thermometer is a thermometer telling you nothing at all. Change it as soon as the display starts to dim rather than waiting, and check the reading against a second thermometer occasionally to confirm it has not wandered.

Good questions

Before you buy

About ±1 °C, which is normal at this price. It is reliable for spotting change rather than for calibrating equipment. If you need a precise absolute figure, check it once against a lab thermometer and note the offset.

Yes. The probe and its lead are made to sit in the water; only the display needs to stay dry. Run the lead over the rim rather than pinching it under a lid.

At the opposite end of the tank from the heater, and not right beside the filter outlet. Next to the heater it reads the heater, not the tank.

Around a degree in absolute terms, with resolution to a tenth. That is fine for aquarium use, since you are mostly watching for change rather than needing a precise figure.

Yes, that is how it is meant to be used. The electronics are outside the tank and only the sealed probe sits in the water.

At the opposite end from the heater, at mid-depth, and out of the filter outflow. Beside the heater it reads the warm plume rather than the tank.

Last reviewed 30 August 2026

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