It sounds like diatoms. Is it dusty and rust colored? If so, diatoms are a normal phase that most new tanks go through. There isn't much you can do about it, and they are not harmful.
If your tank has finished cycling, you can add some sand stirring snails such as nassarius snails.
If you are using tap water, that will continue to contribute to the diatom problem. You should switch to RODI water.