It's important to know that the warmer the temp in the water the less oxygen there will be. Goldfish
are heavy consumers of oxygen, thus don't tolerate warmer temps very well.
Before putting medications into a tank it is IMPORTANT to properly identify the illness issues. It is also important to read the ingredients on medications, as not all meds are safe for all fish. There are many ick treatments out there, but only a few that are truely safe for Goldfish
I would suggest adding carbon to the tank for 48 - 72 hrs, doing a 20% water exchange, and let the previous meds filter out of the tank completely before attempting to medicate again.
Something else that is vital is to know your water quality stats, as any ammonia or nitrite could make the meds have an adverse effect, and high nitrate can do the same thing.
, I would suggest formailn alongside methylene blue to treat ick. This should be quite safe for your minnows, but it will turn the water blue throughout the treatment period. Treat as instructed on the packaging.
I hope this helps!