I used one for several years to dose fertilizer in a planted tank. They actually work really well when you get it programmed. It has to be mounted outside the aquarium hanging over the back of the tank (away from lighting). It just rotates a small drum filled with liquid to dose into the water. Each dose is 1ml and you can dose up to 8ml per day of a liquid by setting the timer.
I guess you could use it to auto dose just about any liquid to the tank.
