Ok so here is what happened. I started a fishless cycle of my freshwater tank. Weeks into it, the pure ammonia I added began to dissipate. My nitrite and nitrate were still measuring zero. Whenever the ammonia level became almost nothing, I added more and brought it back up to 2-4ppm. This went on for over a week and still my nitrite and nitrate levels were reading zero. On the advice of a helpful chatter here, I shook nitrate test bottle #2 vigorously and retested. Turns out, I missed that in the test kit directions. So sure enough after shaking the bottle then testing, it finally showed the presence of nitrate. The level was through the roof, crazy off the chart high. So I did a 99.9% water change, and the nitrate level dropped to a measurable 20-40ppm. So I did another 99.9% water change and still I’m getting a reading of 20-40ppm of nitrate. I thought a total water change would bring the nitrates down to zero. So my question is where is the nitrate coming from? Also, if I shut down tank and just let it sit for a few weeks, will the nitrate die/go away? If not, I assume I need to completely empty the tank, toss the filter media, rinse everything well, and totally start over? Thanks for the help.