The Tunze Osmolator is a great ATO controller. It keeps the water levels in the tank at the perfect level. This item is actually just a replacement controller. It is needed when you have damaged something. In my case, the optical sensor got too scratched from years of cleaning hard water deposits. It sure would be nice if the sensor itself could be replaced instead of the whole unit. Either way, still good value in reducing the maintenance needed to keep my tank at ideal levels.
