Phosphate

[Popeye]

My 180 has been running for about 4 months and my phosphate levels are not decreasing. Two weeks ago I added a phosphate reactor when my readings were .20 last week my readings were .15 this week though my readings are .17. I do weekly 10 gallon water changes, I am using R.O. My fish and corals seem to be fine. Initially i had a problem with hair algae but my clean up crew fixed that problem, Then the dreaded diotom algae on the substrate which has decreased significantly but is still there. My skimmer is working overtime and I'm cleaning it out every other day. Any Ideas?
thanks