4 months ago my nitrate levels were around 10 ppm. My corals were also green or browning out. They got a little better when nitrates dropped to 4 ppm. In the last 3 weeks, my nitrates went down to 2 ppm. Purples and reds returned. I slowly added vinegar to my system. I am not there yet, but am doing this nitrate reduction thing very slowly. Hope this helps.