I just started using my new ebo-jager heater (75W) in my 20G long tank. I set it to 74-75 degrees and noticed that the indicator light would turn off after at most 5 minutes and the heater would start to cool down. This would happen when my water temp was definintely colder (at 71C) than the set temp. I tried turning down the dial 3-4 degrees as suggested in the manual and then turning it back up to 75 degrees. Then the same thing would happen. Has anyone encountered this problem with ebo-jager before? Thanks a lot!