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The pictures are a bit big. Its hard to tell. Is the stuff growing IN your heater or on it? Nothing should be growing IN it. If it is inside there is probably a leak and you need to get it out of there asap. Is the white spot on your gourami fuzzy looking?
Looks to me like it's a gourami that's growing there, haha j/k.
I think it's some kind of algae or diatom. How long has the tank been running? Is it cycled?
They look like mineral deposits, to me. You could try cleaning the heater with a little vinegar soak and then a clean scrub-brush and warm water. If it's mineral deposits, it is most likely calcium and should come off nicely with the vinegar.