So, I've had my tank up and running for about 4 months now. It fully cycled 2 months ago. I usually do water changes once a week (about 10-25%). So, anyways, I had to move the tank as I moved in order for school to start. Since I've been here, my readings have been very odd. I never seem to develop any nitrates. I have been running tests for ammonia, nitrites and nitrates every week and haven't seen anything at all develop. Not only am I not reading any nitrates, but no ammonia and no nitrites. Why could this be? Could there be some form of nitrogen fixing bacteria in the water here? I know that type of bacteria is necessary for salt water tanks, but I have a freshwater tank. The tank in my girlfriends' apartment is giving off fine readings consistent with our water changes. Nitrates go up, we change, they go up again. Just how it should be. Any help?