ive been running into the ammonia reading issue for the entirety that my tank has been going. as of about 2 weeks ago, maybe 3, my nitrite readings have finally gone to 0 and have stayed that way. however, ammonia has never been zero. the highest i ever saw it was .5, but that was one time, and ever since it has been .25, including the test i took today.
i test very often because i am a worry wart, but it has never seen zero. i will also add that it has never had an actual reading below .2 with any test kit. i bring my water to the LFS, and they see the same results. i have 2 test kits myself that i use. one an API (test result picture shown below) as well as a red sea test kit. the red sea shows .2, but you can get the idea that it is basically the same as the API.
below, i also included a picture of what 0 in a red sea should look like so that you can see the contrast between a positive reading and a negative reading, look like with this kit.
although i have a .25/.2 reading every time, i have also had fish in the tank for at least 5 weeks with those readings. i have been adding slow to ensure that my ammonia doesnt jump. i currently have a diamond gobby, 2 clown, 1 bi color blenny, and a cleaner shrimp, and none of them show signs of distress or danger that one might expect with ammonia. the one thing that i have seen is that over the course of the last 3 weeks, the shrimp has molted twice, but he is also young, so i chalk it up to growing. the gobby has been in there a week, and is acting normal now that he is beyond the shy stage.
i put up my predicament on R2R last night, and got the same kind of responses that the LFS said, so i feel safe with the current status. i know that the water readings without being in a tank are 0, something within the tank is creating the .2 reading. however, at the same time, the fish as thriving, so if fish arent dying and there arent any bad things going on, no need to worry so much.
in the end, i dont think my readings are misreadings so much, since they are confirmed on 3 seperate tests, but i do think that having a reading of .2 is not necessarily something to be worried about unless you are running into livestock problems.
p.s. its a 20 gallon tank