I would be much more concerned with the effect of the salt on your fish than your plants. Characins are very sensitive to salt. I would never under any circumstance put salt in an aquarium containing characidae, corydoras, most acidic water catfish, or plants.
I normally stay out of discussions on diseases because I have very limited experience, but ich is one I have had my share of over 20 years, more than I should have. When fish are fighting off a parasite or disease, they are under stress. Doing anything
that elevates that stress is bound to make it worse. For this reason I do not adjust the temperature; higher temp will speed up the parasite cycle, true, but it also adds to the fish's stress, in varying degrees depending upon the fish. Corydoras panda for instance would find 82F intolerable and quite possibly die from that alone; is that worth the risk when there are safer methods?
Salt is another stress source; it does have an impact on the fish's physiology, as indeed will many medications for ich which usually contain copper, a toxic heavy metal (which will also affect plants if strong enough). Characins are particularly sensitive to chemicals, salt, medications. Most ich remedies recommend half-strength with tetras, this is why. Corydoras are in the same camp.
My successful ich treatment is first to leave it alone. Provided the aquarium is established and balanced, the water parameters are within the preferred range for the fish, and they are healthy, they will easily fight off ich if it is introduced. My last two cases of ich (the last was 4 months ago) have just disappeared on their own.
When it is especially heavy, I use Aquari-Sol for 5 days. Then I do a 50% water change. I have cured heavy infestations and never lost a fish. Heavy infestations are rare, in my case usually only associated with new tanks which, as mentioned, are not established and balanced and thus the fish are under stress already, hence the ich is able to take hold more. I use Aquari-Sol because it is recommended for sensitive fish, and in my experience, although it does contain copper, the sensitive fish show less stress with this in the water than anything else I have tried.
If you only see a couple of spots on one fish, leave it alone. Provided everything is fine in the aquarium, it will dissipate and the fish will be stronger for it.