My 40g is fairly new, the tank has only been set up for a few weeks now, since (I think) July 20th, 2015. I do partial water changes (10g) every day or two. I noticed some of the fish seemed stressed on Monday, did a large partial water change (20g), followed by another 15g pwc the next day, 10g pwc yesterday, and a 10g pwc this morning. After this morning's PWC, about two hours after, I tested the Ammonia, NO2, NO3. Ammonia was 0ppm, NO3 was (I think) just above 0ppm, the color was a closer to the 0ppm than the higher reading. The NO2 came back very dark (5.0ppm). Is it possible that this was a false positive reading? The fish seem totally fine, swimming around actively and not acting abnormal in any way. I use TopFin brand water conditioner (5 ml to 5g) to pre-treat my water (roughly 25 minutes prior) before adding it to the tank. I also use MarineLand EasyCare, 2.5ml in each of my 5g buckets. I tried searching around on Google and couldn't find anything for either of those two treatments relating to nitrite. Figured I'd post this here and see if anyone could provide any insight. It just seems impossible that the nitrite could be that high without the fish suffering significantly and showing signs of it, especially after all those water changes.