I have an Eheim Jager 50W heater in my 12 gallon long aquarium. It used to be able to keep my tank warm, but now it doesnt seem to be able to maintain steady temperatures. It used to be rock solid at 78, now it fluctuates wildly, and the light is always on, so its always working. Do these things loser power after a while? I've had it for about 2 years now. What are other people using in their 12 gallon longs?