Have you ever checked your
PO4 level?
PO4 is one of the biggest "feeders" of algae. Does your
RO have a
DI stage? The
DI stage removes most of the
PO4.
Also how much do you feed and how often? Do you drain the packaging juice from the frozen food before adding?
How long is you lighting period every day? Do you have a skimmer?
Its most likely diatoms and they should go away eventually, but nutrient control is the key to elimination.