Perhaps a picture of this stuff closer up on the back glass corner would
get you an ID on it.
I've never heard of (or seen any) nuscience algae being white so maybe it's a type of fungus
I am not sure what to tell you, some of the other members may have better ideas.
If it's not affecting or caused by your water parameters, maybe it will just run it's course & be gone.
Your TDS should read zero coming out of your RO-Di system.
Are you still dealing with cyanobacteria?