I currently own this top rated ATO and it has never had any issues. They don't go on sale often, so snatch one up!!


* High-tech top off system for precise control over aquarium water level

* Automatically replenishes aquarium water lost through evaporation

* Inclusive kit comes with control panel, optical & mechanical sensors, magnetic mount for sensors and water pump

Proper aquarium water level is more than just aesthetics, it's a health issue. Tunze Osmolator Universal 3155 Auto Top Off System was developed because Tunze knows the health of delicate aquatic life requires constant osmotic pressure. Short for Osmotic Regulator, the Tunze Osmolator is a high-tech auto top off kit that comes complete with an electronic control panel, optical and mechanical sensors, magnetic mounts for the sensors, water-metering pump and accessories to streamline installation. All you only need is a reservoir to supply constant water level in your aquarium!

Tunze Osmolator Universal 3155 Auto Top Off System boasts German engineering featuring an optical sensor that precisely recognizes the water level. Manual float switch provides backup security by shutting off the water metering pump and sounding an alarm should the optical sensor fail. If the backup fails, the pump is shut down after 10 minutes to prevent any potential over flow. Electronic Controller performs a self diagnostic when switched on and features colored LEDs for simple visual confirmation of operation.

Why topping off your aquarium is so important
While we see low water level as an aesthetic nuisance, your aquarium inhabitants experience something dramatically different. Low water level due to evaporation means higher concentration of dissolved chemicals, including salt concentration. Sensitive marine fish, corals, invertebrates and other delicate species may be affected by this change in water parameters and osmotic pressure. The Tunze Osmolator ensures the accurate and safe compensation of evaporated water for osmotic stability in freshwater and saltwater aquariums.

Downloadable Tunze Osmolator Universal 3155 Instructions PDF.
(Requires Adobe Acrobat Reader 4.0 or later - get it here for free)