Perform a partial water change immediately

Use dechlorinated, temperature-matched water

Reduce feeding for a few days

Remove uneaten food and waste

Clean debris from the substrate

Check and clean the filter media in tank water

Add beneficial bacteria starter

Increase aeration and surface agitation

Test water daily until ammonia is zero

Stop adding new fish

Reduce stocking if the tank is overcrowded

Make sure the filter is properly sized and running

Use ammonia detoxifier if needed

Quarantine sick or dying fish

Avoid overcleaning the tank and filter

Maintain regular water changes

Monitor pH, since higher pH increases ammonia toxicity