What are your other readings and what are you using to test your water? Besides ammonia you still have to worry about nitrItes and nitrAtes. NitrItes are just as deadly to fish as ammonia and high levels of nitrAtes can also kill.
Also, using those test strips to test your water can lead to a lot of headaches. I would recommend using the liquid test kits. They're much more reliable and, in the long run, cheaper.