I've got one, it does have adjustable levels but based on the design, you get more per feed when you first fill it and less as it empties. Mine will either sit on the tank/light/filter/whatever flat surface or you can clamp it to the tank. It works fine but it feeds twice per day, and my lights aren't on for a whole 12 hours so I'm not sure if the fish come out and get stuff for the second meal (this is the SW tank, so the fish aren't out when the lights are off).