I understand your situation, Debs... but it would be a better idea to isolate and just treat the affected fish right now. Bacterial issues can be transmitted (b/c bacteria is ever-present)... but for whatever reasons... the other fish's immunity is more intact to prevent them from being affected... so treating them with an antibiotic if they're otherwise healthy could lead to future resistance issues.

Kana would be a good choice... but we recommend cutting the dose in half and administering every day rather than the suggested full dose every other day. If Kana isn't available to you... then MII (possibly with plain Maracyn) would be the next choice.

You may need to do 2 rounds of the med to notice any results (if this is bacterial in nature)... so just be sure not to skip any days between doses...and don't double the 1st dose of the 2nd round. If you don't notice any improvement (or he gets worse) on the meds... then it's likely a viral situation.

Let us know how he does! Good luck!

Michele