In my two years of fish keeping, I've encounter ich (came with the fish), gill fluke (came with the fish), mouth rot (came with the fish).
It is most important to use a quarantine tank for new fish before adding them into the existing aquariums. No disease will just come out of no where. There is always a source, and they usually come with already infected new fish you just bought.
I would not recommend to use any medication for ich though. Heat treatment alone cured my fish in less than two weeks. All I did was simply raise the water temperature to 86F slowly. Most ich dislike high temperature and they will just die eventually.
Some medications did more harm than good for me, and I am not going into that part lol. Terrible memory.
For mouth rot, I spent so much money on getting the poor Neon Rainbowfish cured. Took me months to get them healthy again. It was horrible to see their mouth rot away, not my fault though since they came with it. I only blame myself for not seeing that before I bought them from Pet Supplies Plus (dirty water, terrible lighting, so I couldn't see it until I set them in my quarantine tank).
My advice is, it is best not to use medication on the first sign of problem. Some of the problems can be fixed without the use of medications. Medicates all have side effects, sometimes they can ... kill the fish. <--- Speak from the experience !
Heat treatment can be effective for ich, depending on the type of fish. It's not always as easy as turning up the heater in order to help out as many fish can stress/die from rapid temp fluxuations. Of course, the blame generally goes to the disease in cases like that. Nothing above a degree per hour/hour and a half is really recommended, as the fish have to acclimate. Thats where my infrared thermometer comes in handy
I have two fish, Leporinus Fasciatus, that are very sensitive to tank heat fluxuations. Their tank is heated and has a thermometer, of course- but I can usually spot a temp related issue immediatly because their color drastically changes with any variation.
Too warm, they're too gold. too cold, their black fades
Maybe you do not even need a thermometer lol. The fish themselves are more accurate thermometers from what you told us.
It took me a day to raise the heater to 86F from 80F. I know fish would only adapt if the temperature change gradually. That was a while ago though. Ich never came back since they would not come out of nowhere.
The ich I got was from the fish shipped to me by Petsolutions.com, and it quickly spread to most of the fish from what I could see (probably all fish, but most ich symptoms hide under the gills)
The fish from liveaquaria.com were of higher quality with only 1 fish came with cotton like fungus on one side of its body and it died overnight.
Always use a quarantine tank for any new fish is the way to go.