What sort of algae is this?

[Ian]

I'm not an expert but I do know that one issue with testing your water is that the algae itself can use up the nutrients which then gives you a reading that seems "fine". if the algae is growing winnning vs your skimmer and cheato you have to be providing it with food to allow this. Without fixing that you will continue to have an algae issue .

Looks like a hair algae to me. Hand pick as much as you can, pluck it from the rocks and "vacume it up when you do your water changes also. Find and eliminjate the source of the nutrients its using. Do more water changes but be sure your R/O is not in need of a filter change.