Just slow down and think things through. I would not a a broad spectrum antibiotic because guess what, your filter bed is loaded with nitrifying bacteria. These will take a hit. Put a good ion scavenging media in the sump such as Chemipure or just activated carbon. Get all traces of ammonia and nitrite out of the tank by chemical filtration instead of frequent water changes. Fish are hardy and can recover as long as they are not subjected to constantly changing chemical and pH parameters. Good luck.


