How long has the tank been running? If there's ammonia there, the cycle isn't finished. Sometimes they go weird, though, especially if you used a bacterial supplement product and were lucky enough for it to work. A constant ammonia level like that can mean the filter is underperforming, or possibly a faulty test kit. Take two samples, test one and record the results, and take the other to the LFS and ask them to test, then compare their readings to yours. If any of their results don't match yours, just replace that test (depending on what test kit you use, you should be able to buy the tests individually instead of a whole new kit).