I finally broke down and picked up a Hanna low range phosphate tester (after turning off my GFO several weeks ago). I am testing at .009. Based on what I am reading, it should be closer to .003? Does it make sense to turn the GFO back on, with half the media? I do have a very slight hair algae problem, if that matters. Just want to make sure I don't make any wrong decisions based on the reading.