Your water quality was good when you had a die off? That doesn't sound right. If you lost a lot of fish there are only 2 possibilities: 1) ich, 2) ammonia poisoning.
The ammonia is supposed to go to 0 before you add any fish. You should only add 2-3 fish at a time to start an aquarium. You have to do a lot of water changes and wait for the bacteria to establish themselves.
Have you tested the water you treated with the ammonia remover? If even that is bad, I would suggest using spring water in your tank.
If all of your fish are dead, then you should just let you tank sit until you get the ammonia under control.
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Phishie

"An ounce of prevention is worth a pound of cure."