If the ammonia level is greater than 0 and is considered toxic for the PH and water temp you can:
1. Use an ammonia binder (Prime, Amquel, Amquel Plus, Ammo Lock, Chloram-X). Ammonia binders do not remove ammonia; they simply convert toxic ammonia to a nontoxic form. It will be effective immediately, but will only remain effective for 24 - 48 hours. Need to add again. Ammonia test kits will still test positive for ammonia, even though it is nontoxic. The biological filter will then consume the nontoxic ammonia, converting it to nitrite and then to nitrate.
2. Stop feeding the fish (because this causes them to create more ammonia).
3. Perform a partial water change.