Experts agree that aquarium stability is absolutely essential for maintaining a saltwater aquarium, and that a few things can throw off your reef tank’s chemistry like water evaporation, thus, endangering your fish corals. This is what makes an auto top off system—or ATO—an absolute necessity for any saltwater aquarium. (In fact, an ATO is the # product to make your aquarium lower maintenance.)

As water evaporates from your aquarium, the ATO replaces the water lost from your system with fresh water from the nearby reservoir thereby maintaining your reef’s stability.

The Osmolator is one of the best-selling automatic top-off units in the hobby, and for good reason! Tunze is one of the most trusted names in the aquarium industry, in fact Tunze invented the ATO about 30 years ago and they have been perfecting it ever sense.

The Tunze Osmolator is an all-inclusive state-of-the-art auto top-off system and includes everything you need right out of the box to be set up in as little as 5 minutes.

Included with the Osmolator is the pump, fill hose, hose mount, control box, both the optical and the float switch sensors, multiple mounting options, and power supply.

The small but powerful DC pump included with the Osmolator is capable of pumping water to a max head pressure of 13 ft. This is great for applications where the reservoir may be located in a basement or some other remote location separate from the tank.

Unlike other pumps with side intakes that run dry without fully utilizing a reservoir’s water capacity and thereby requiring more frequent reservoir refills, the Osmolator’s pump draws water from the bottom to use the full volume of the reservoir and help prevent dry run.

The Osmolator comes with two sensors: one optical sensor that digitally detects your water level so that the pump is activated when the water falls below the sensor line, and number two, a float switch which operates as a failsafe in case the optical sensor becomes unable to detect the water level due to obstruction or some other malfunction.

The sensors can either be mounted together on a single magnet or you can utilize the provided second magnet for mounting the float switch in a separate location if you prefer.

In addition to the failsafe provided by the float switch, the Osmolator is equipped with an electronic monitoring system that monitors how long your pump is running and shuts it off after 10 minutes of operation along with sounding an audible alarm to alert you that your system has been running for too long—which may indicate a problem with the sensors or (more commonly) that your water reservoir has run dry.

The control box of the Tunze Osmolator is equipped with LED indicators to notify you when your water level is too low, when the pump is on, when the water level is as it should be, and when the water level is too high.

Some aquarists may be surprised to find out that the Osmolator will not integrate with any controller currently on the market, so you aren’t able to communicate to the Osmolator remotely. However, most aquarists won’t find this minor limitation problematic as the Osmolator controller offers plenty of options for control built into the unit itself.

By going into the box, you can adjust the power of the pump to increase or decrease output and head pressure as needed.

You can also adjust the alarm so that it sounds when the backup switch and maximum run time are both triggered, anytime the backup switch is triggered, or even to turn it off completely so that it never sounds. Which we don’t really advise doing.

Additionally, there are a number of accessories which can be purchased separately for use with your Osmolator like the water storage container (which functions as a 7-gallon reservoir for your Osmolator), the Tunze Osmolator Calcium Dispenser which allows you to use your Osmolator to distribute kalk directly to your system without needing a separate kalkwasser reactor, the solenoid water valve (for direct connection of your Osmolator to a separate water source, or the switch socket outlet (which allows for swapping to most any AC pump available).

All in all, the Tunze Osmolator 3155 is an excellent addition to your aquarium gear and is built to last for many, many years. Thanks for checking out our video! If you found this information helpful, please subscribe to our Youtube channel below. Until next time, take care and happy reefing!