Algae problems continue

I have been fighting hair algae for about a month now. I have been doing 25% water changes twice a week and cleaning the sand very well. My protein skimmer continues to produce dark dark green, nearly black skimmate with plenty of "chunks" or bits of stuff in it. My nitrates test over 160 and they wont go down, I would think that that test kit is wrong, but hair algae continues to go. I purchased a lawnmower blenny and he has been eating his little heart out. He has put on a good amount of weight since going in the system. 2 emerald crabs pick at the stuff day and night. A horseshoe crab turns sand over daily. I wake up to clean sand but as the day goes on, diatoms gather on the sand but they get turned over or sucked out in the water changes. I have no idea what to do next to get the nitrates and possibly phosphates down. Also when I add my RO water it gives an "oily" look to the water, what is causing that. Please help me out.