I have a Waterbox Reef 220 tank which will be 6 months old this month. Live rock in the tank is from a previous established tank. Nitrates in the 220 are testing at 40 ppm. Can't seem to get them any lower. I have a refugium which is keeping Phosphates in check but not the Nitrates. Phosphates test out at .25. Medium bio load in tank. Nyos 160 skimmer. Doing weekly water changes of 20-30 gallons. What else can I do to lower my Nitrates? Currently I am not running any media in a reactor. Suggestions?