I have had this tank cycled and well established for over 3 months, and have had this white substance in the tank for 2 of those months. It is a 10 gallon planted tank with aquarium sand and root tabs. I only have 2 male bettas in the tank (divided).
It is all over the sand and appears somewhat fuzzy. I vacuum as much of it up as I can once a week and it always comes back. I am not sure what else I can do so I am hoping someone can tell me what it is so that I can figure out how to get rid of it.
I'll post some pictures in a few minutes.