I always feed antibiotics like kanamycin, unless the fish isn't eating. I would suggest mixing it in the mysis, freezing again, feed 2-3x/day, small amounts. Sometimes I used Focus from Seachem to bind the med to the food.
I too seem to be a magnet for diseased fish, but I've healed many of them, helped locals save theirs and now I find it interesting and read fish disease textbooks in my spare time.
A few pointers that come to mind are: keep QTs at least 10' apart from each other or the main tank since disease can become airborne and spread. Make sure you wear gloves when dealing with meds, most of it is carcinogenic & only treat when absolutely necessary - use TT instead of copper for ich. If a fish has a small infection, that doesn't look like septicema, sometimes it's best to leave the antibiotics in the cabinet for a bit and see if the fish's immune system will improve the condition. These are my opinions and I like them because they work for me. I used to get all worked up, now I take a more relaxed approach, do a lot more observing for change/symptoms, medicate sparingly & have better results.