As Steve mentioned, Prime or Safe or Cloram-X will bind the ammonia into the non-toxic ammonium form, but to know if you have enough binder to keep it converted, you really need to get the SeaChem Ammonia Alert Card. It will show the toxicity of the ammonia from safe to lethal, and as long as it is in the safe, then enough of the binder is present. The test numbers are important for evaluating the stability and safety of the water. High ammonia burns the gill tissue and skin, making it hard for the fish to take in oxygen, or for burnt skin, flashing. KH is probably the most important test, at least for cycled filter systems, as the KH is consumed by the filters and when gone allows extremely wide swings in pH from very high to very low, causing irritation to the fish, but also the pH crash will kill the bio bacteria that convert the ammonia to nitrite and nitrite to nitrate, creating high ammonia levels even without feeding.
Melafix generally is not considered to be of much help. It is a tree oil and oil and water really don't mix well and oil coating the gills will impair oxygen intake. It is not an antibiotic which is needed for most ulcers. It does make good money for the seller and manufacturer.
Zone 7 A/B
Keep your words sweet. You never know when you may have to eat them.
Richard