Start doing some water changes and running some Carbon for starters. That should help neutralize chemicals in the water (if it is chemical contamination).
Also, since your fish are already that sick, it will be difficult to move them to another tank where you can treat the ick without stressing them out even more so. Do you have any corals/inverts in your tank? Did something die to cause the ammonia spike? How did the SG get so low?
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