Mechanical aquarium Automatic Top Off system / Automatic water level control (ATO) for aquariums and other liquid containers. Aquarium ATO system is especially useful in marine aquariums where unfavorable changes in water salinity due to evaporation are dangerous to the aquarium life. When ATO system is used, fresh water does not need to be added daily, which makes reef aquarium maintenance much easier.

This ATO system is mechanical without any electrical parts. A float lever will mechanically close and open a valve in a replacement water tube when aquarium water level changes. Water is fed into the aquarium by gravity, hence the replacement water container needs to be positinoned above the aquarium or sump. As the system has no electrical sensors or a water pump that could jam or malfunction, it is very reliable due to its simplicity.

Float lever is attached to the top of aquarium glass wall with an adjustable bracket (max. 19mm glass). Float lever position is adjustable vertically (up to 16cm) according to the water level in the aquarium / sump.

Float lever is connected to standard 1/4” PVC tubing (same tube is used in RO-filters). There is 200cm of tubing included. Tubing can be connected to a valve that is installed through he bottom of a replacement water container or the tubing can be put over the edge of the container and used with siphon principle.

Mechanical ATO is an economical option for automatic water lever control, but in order to be reliable, the float needs to be much larger than an electronic ATO's float sensor (the float is 82mm long). As ATO float should be in a place where water surface does not wave, this ATO is preferably used in a sump or the float should be otherwise protected from surface waves, for example by enclosing it behind a suitable wave barrier. Due to its size, this ATO can therefore be difficult to use in very small nano aquariums.