Hi Grace,
How long have you had your fish in your aquariums? Did you cycle them before getting the fish?
When you say high ammonia, what is the actual reading?
The first thing we usually do after a high ammonia spike is to do large percentage water change of up to 70%. It should lower the ammonia temporarily. Do it twice in a row can decrease the ammonia concentration to relief some stress on the fish. Make sure to use a gravel vaccum to remove any debris such as leftover fish food and fish waste at the bottom since they are sources of ammonia.
A few things not to do. Do not wash the filter or filter media (as well as gravel and decorations) under tap water, or you might damage the good bacteria colony. The only true way to end an ammonia spike is to restore the good bacteria colonies. It takes time for it to happen. So the last thing you want to do is to damage the bateria colony further.
Stop feeding the fish for a few days, and feed the fish with reduced amount only once every 2-3 days. Feed them no more than they can finish within 30 seconds each time. Reduced fish food means reduced ammonia being produced in the system.
Some other emergency measures include getting Seachem Prime for partial water change. It can temporary turn ammonia to relatively harmless ammonium for up to 48 hours. Keep doing partial water change every day with Prime will minimize the ammonia damage to the fish.
Getting a bottle of live bacteria product such as Tetra Safestart will also help to get the aquariums cycled again faster.
If you have any further questions, feel free to ask.
