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There are a number of "fuzzy white things" that can show up that are perfectly normal, but we'll need a little more information to tell what it is you have. How old is the tank? Can you snap a picture and post it here, if not what size and shape is it?
You can update "my info" with your tank size/equip and critters, that will help in future posts, if you like. I just noticed some sponges forming on my LR, just like that. I had id grow after my tank cycled but my urchins seemed to have munched it.