Start doing 20 gallon or 30% water changes once a week, checking your TDS from your R/O System to make sure your make up water is good. You need to get your calcium and Mag levels up hopefully water changes will take care of this in time. Remember your tank did not get that bad over night it took years and will take at least 6 months to straighten out. Next two choices, either softies like Xenia and GSP, and or a phosban reactor with phosban to remove undectectable phosphates. That is what I call them when you buy a test kit and everything looks good but you still have hair algae? Good luck just remember it will take months to change your tank