Did something die that you do not know of? How much are you feeding? Was anything added just before the high levels of ammonia appeared such as new rock, inverts, etc....? How many/what fish do you have in the tank? Any source of filtration (live rock, filter, or fuge)? What are the water parameter levels as well? As of now, just do 25% water changes every other day to see if that will help bring the ammonia down.