I've been having similar problems with my 55gal tank.
I got rid of the cyno algea by getting a better/more powerful lighting fixture and that cleared up in about a week, but then the hair algea just bloomed like there was no tomorrow.
I followed the suggestions expressed earlier in this thread about removing the rocks individually and scrubbing them. It has helped some but it's starting to come back.
My tests last night showed 0 Nitrate, 0 Nitrites, and 0 phosphates. I have a feeling I was over feeding but I'd curbed that back significantly over the past week or so.
At this point i'm doing about a 10% water change every other day.
I have 1 turbo grazer snail and a yellow tang which nibble at the algea but neither make much of a difference against so much of an infestation. I'm considering getting a lettuce sea slug to help out, but I really want to fix the problem at its source, not just getting something to deal with it.
What's causing all this aglea growth? ahahhh!!!!
also, how would I go about testing my RO water for silicates? do i need a special test kit or is there somewhere that I can get it tested at?