Hi Anna - I had that same problem with my Ebo Jager, but the big greenie as they were called, which I bought in '93. No matter what I set it on, the tank temp kept climbing. I immediately replaced it with an Otto Computherm heater and controller which is still being used today. The only thing that Jager was good for was stirring water in a barrel, especially since it was soooooo long! I recently bought the Rena Smart Heater to replace another failed Stealth and so far, its been extremely steady and I'm very happy with it. I'm using it as a stand alone heater now in QT, but when I'm done with it I'm going to replace the intake of my XP3 with it, and set it lower than my Hydor ETH inline, (which I highly, highly recommend if you're using a canister) just in case the Hydor ever fails.