I am running a Fluval FX4 on a 125 gallon African Cichlid tank. Currently have 12 fish including Mbunas, Haps and Peacocks. My nitrates seem to be higher than what I would expect. I do a 50% water change weekly. My nitrates are at about 60-70 ppm each time. A 50% water change only gets me to about 30ppm. I recently started doing water changes every 5th day to keep things under control. I do feed twice per day however. I am considering placing Matrix in my filter to see if that might help reduce my nitrates or at least get me back to a 7 day schedule. Is anybody using Matrix with any success?