heater
I don't know what kind of water you have...hard, soft, ect... I have hard, alkaline water here and I have that trouble even if the water levels don't drop too low. All water has a certain amount of minerals in it. These minerals seem to condense (for lack of a better word) on anything warm. Heaters seem to really attract it! Try cleaning the glass part with white vinegar. If it won't come off, let it soak in the vinegar for a while...maybe overnight. I wouldn't soak the top of the heater as I don't know what effect the vinegar might have on the seals, but it won't hurt the glass at all. Vinegar is the best thing I have found to remove mineral deposits on glass or anything else for that matter. I use it to clean the glass on the outside of the tanks, the heaters, and the glass tops. A mild vinegar and water solution works better than the ammonia based cleaners like Windex IMO (don't use these on aquariums).
Logan J
