did you get more angels while the quarantine tank was in use?
Adding fish to your 55g w/out quaranting is such a gamble. How many did you get and where are they? is your 10g cycled yet? if not I wouldn't put any fish in it. This might be a bit expensive but i'd just treat the main tank if you are having fin rot probs with more that one fish and it would probably get worse if exposed to ammonia and such. don't you think?
I'm actually doing that right now. my quarantine tank and hospital tank are both being used and i noticed one of my plecs with a scrape and angel with a little bit of fray so i'm dosing the whole tank with pimafix just to be on the safe side. (i really gotta separate these fish, total scrappers)
i'd be more afraid of the evil ick
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from the new fish (but i'm wicked paranoid).
good luck to ya!