Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Ditto Raymond S.
Add the bacteria your tank needs. Your fish may be hardy enough not to die, but the toxins can be shortening their lives, and harming their immune system.
The right species of bacteria can be found in bottles that specify Nitrospiros species of bacteria.
Do a big water change to get the ammonia as close to zero as possible, and add the right amount (or more) of Tetra Safe Start, Dr. Tim's One and Only or other source of Nitrospira. Save the rest in the fridge and add some each time you add new fish.