I have a 46 gal with about 50 lbs live rock. The tank has been running for a year and a half. I havent added anything in a couple of months, nor has anything died. My tests have always been fine, but recently I'm having problems with nitrates. They keep testing in the 40 - 80 range. I do 25% water changes every other week. When I do this, water tests down to 10 - 20 range. Following week tests 20 - 40. Then right before water change 40 - 80. I have a penguin 330 filter with bio wheels. It seems I've read here before that someone said that bio wheels attract nitrate or something, and that they shoud not be used. Is this true and do you think this could be my problem?