Water Problems, please help
I have some issues with my nitrates. I tested my tap water about 2 weeks ago and found 15ppm in my tap water. Ok, so use this water for water changes and continue to test my tank water. Nitrates were holding steady at about 12ppm in the tank. I continued my water changes (the last one was Friday) and added a canister filter with media from my old Aquaclear. Today I tested the nitrate levels in my tank and they were at 0. So I decided to test my tap water again and that is also now at 0 when it was at 15ppm 2 weeks ago. I then took a sample of my tap water and added Flourish Nitrogen, retested and found out that my test kit is working. What's going on and how quickly should I up my Nitrate level with Flourish Nitrate?