Review: Hydor Smart Level Control


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Levi Major checks out this new automatic top-off unit from Hydor.

It’s good...

It’s taken a few years of development, but finally Hydor have turned their attention to the all-important aquarium water level control and the Hydor Smart Level Controller is at last ready to enter the Automatic Top-off (ATO) market.

This ATO unit is meant to monitor the water level of a sump or aquarium and starts a top-off pump when the water level falls to the set minimum level. The Smart Level controller can handle top-up pumps up to 50w (not included), though for top-off purposes, this is a little excessive unless you have a very large aquarium.

The Smart Level probe has three ports that indicate a maximum and minimum water level, as well as an alarm level, all of which have indicator LEDs. It is purported that the unit operates on temperature changes that occur when water fills the probe chamber, causing it to turn the top-off pump on or off as needed. The probe has a magnet/suction cup hybrid mounting system, with additional cable clamps to keep the probe horizontally positioned and the magnet can handle a wall thickness up to 10mm.

Hydor’s Smart Level technology has been designed to reduce the problems related to scale deposits, bacterial film and wave action, thus theoretically ensuring the continuous, safe and regular functioning of the Smart Level control.


Although it’s ultra-compact, easy to install and has no moving parts, I doubt this unit can be used by all fishkeepers. My main issue lies in the fact that the water level needs to drop from where you set the maximum level (i.e. your chosen water level) a full centimetre until the water level reaches the minimum level probe before the unit engages the top up pump.  

Therefore, unless the probe is used within the return pump section of a sump, your system will still be subjected to relatively large swings in salinity. Granted the salinity rise will be gradual and governed by the rate of evaporation; however, the system will experience a rapid drop in salinity as the unit engages the top-up pump and fills the system from its minimum level back to the maximum level.

The verdict

If I had to choose between topping up evaporation by hand or using the Hydor Smart Level Control, I would certainly choose the latter, but I would only run it in the returns section of a sump to minimise the potential salinity swings a cm of evaporation would cause in an aquarium without a sump.

Despite the cost of the unit being lower than the likes of the Tunze osmoregulator, by the time I have then purchased a top-up pump to use, the overall cost would not be too dissimilar to the Tunze, and given the superior optical sensor of the Tunze osmoregulator, the latter would be a preferred option, as it is more responsive and can be used with more confidence whether a sump is installed or not.


  • Fully electronic, featuring dual alarm with light and sound to alert of any malfunction.
  • Insensitive to wave surface movements.
  • Easy to set-up and get going.


  • Only engages the top-up pump following a water level drop of 1cm dictating its use within a sump to avoid large swings in salinity.
  • Top-up pump not included.

Price: £79.99; more info:

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