Are they hard, sort of crusty spots on the glass and plastic equipment in the tank? That sounds like coralline algae ... but Maggie's right. Photos would help a lot with I.D.
It will uptake calcium, so adding a little bit (wouldn't go too hard in a FOWLR) may help it grow faster. When you scrape it from the glass, some of it will land on the rock - and some of that will grow, where conditions are appropriate. No worries.