I seriously doubt you had a kit that is accurate enough to measure as low as .02ppm of ammonia. The lowest reading on a normal kit is .25ppm. Are you sure that is correct? As mentioned, you want ammonia and nitrite (what is your reading?) to be zero all the time. If your tank is new and you didn't cycle it before adding the fish, then you will definitely see some readings. You goal will be to do water changes of 20 to 30 percent as often as needed to keep ammonia and nitrite below .25 ppm. Because you have neons which are very delicate and can not tolerate ammonia and nitrite, it is even more important to keep the levels low.
Also, you need to raise the temperature. Most tropicals need to be in water of 76 ot 78 degrees.