thanks but not sure it is that,it is like fairy floss and it is all over most of my rocksOk, think i may have found it for you. Google - cotton candy algae. It looks like the start of it.
There is tons of info on controlling it. Hope this helps.
This page has a bit about it, but I googled some pics of it and in the early stages it looks just like it. This link has it in the late stage so looks a little different.
https://www.reefcleaners.org/nuisance-algae-id-guide