I had the same in my tank when I first started out. I agree with shift51008, you need to get what causes the issue in check i.e. phosphates that are leaching out your rock, this will subside eventually. I use rowaphos with great success, keep on top of your water changes. You need a trst kit for phospates, do not add any chemicals to your tank what you are experiencing is normal dont panic.
I also used a soft bristle tooth brush to gently aggrevate it off the rocks etc. I generally did this an hour before water change. This allowed the skimmer/ filter to pick up the bulk floating around the tank then i vaccumed the remainder up as part of my waterchange routine.
Anymore advise please message me.
