What's the pH? If it's low, say 6.5, don't worry, wait it out. If it's high, like 7.5, then you've got a problem. Ammonia readings are meaningless without pH.
Bad enough then. Water changes are your friend. And 10% is worthless; it will change 4ppm to 3.6ppm. Try 50%. Then another 50%. That'll bring it down to 1ppm assuming the tapwater is 0. Rinse and repeat.
