Hello; I agree with pops on not treating in a regular tank. A HP (hospital tank) can be better especially when using things like MG.
Many chemicals/medicines can wipe out the good bacteria of a tank. Others are too hard on the fish to have the fish in a long time, thus the short "dip" of say 1 to 30 minutes. Start with the shorter time. I have sometimes dipped a fish in a tank of treated water and kept it in a net the whole time. I usually try a short initial dip unless it is something I have used before.
I saw that you have tried a second treatment with eye drops. This is another potential hazard in that unless you know for sure what disease you are dealing, then throwing more stuff at a problem can be a stress factor.