you should have 0 ammonia i would do a pwc
how long has you tank been running?
are you using a dechlorinator? (like prime for example)
what kind of test kit are you using? you should also be testing for nitrites and nitrates. if you have ammonia, it's most likely that you'll have the other and your tank could be doing a mini cycle possibly. you can pick up a liquid test kit for fairly cheap and it has ammonia, nitrites, nitrates and ph all in one and they are more accurate the strips
from the link i gave you, did it narrow anything down for you?