Post-Cycling Ammonia Spike

Question
I have a 20 gallon fishtank, with 3 Zebra Danios, 3 Albino Corys, and 2
Flaming Gouramis. We set up and cycled the tank in late August, and we
cycled with 4 Danios. The ammonia level spiked as expected, and then came
down to 'ideal' levels per test strip bottle. We then added the other fish, and
the ammonia levels were fine. Recently, a bout of ick hit 2 of the fish, but
resolved with medication from a pet store. Now, the ammonia level is at
'Stress', despite weekly 50% water changes as well as adding Cycle. 2 of the
fish are acting ill. Could we have lost our biofilter? We are not sure what to do
next; can you please help us?

Thank You!

P.S.
We have a filter with a sponge, charcoal, and CycleGuard (Aquaclear 50 gallon
filter) The nitrtrate and nitrite and chlorine levels are "0".

Answer
Hi Matt,
I think you are right about the medication destroying your Bio-filter. This happens all the time when fish have to be medicated. Its a real pain but you can get through it.

The best thing to do is to treat your tank as if it is an uncycled tank. Test the water every day for ammonia and nitrite and make those necessary 50% water changes whenever ammonia is above safe bounds or your fish seem stressed. You can try bacterial supplements but your tank still has to take plenty of time to re-establish the biofilter. You can try using Amquel+ water conditioner to help prevent stress to your fish from the ammonia.

Best of luck and keep checking your water parameters. I hope this helps!
Karen~