Salt at .6% Solution
There are very few times I would suggest these levels be used by the hobbyist, and you are much better off just going with the other medications listed below. No plants will survive this treatment. One of the primary times I use this is for cases of Dropsy. Please refer to the "Symptoms" section of " Koi First Aid".
This solution was primarily used by some breeders to kill the salt resistant protozoan parasites that are primarily found on imported fish, or fish that have not responded to the .3% solution, and are extremely overcrowded. Today however even these higher levels of salt have little killing power when it comes to parasites, and there are better medications available. Again, please refer to the notes and chart above for other important details regarding the use of salt.
Heat
As discussed earlier, heating the water at least to the mid to upper seventies is very contusive to healing. At these temperatures the immune system functions at it best, and when used in conjunction with salt, it will greatly promote the ability of the fish to heal itself. In my opinion, heat is one of the most overlooked aspects of fish first aid when it comes to Koi and Goldfish.
When keeping fish at these temperatures, you should also have some sort of aeration in the water. This is because warmer water holds less oxygen then colder water, and fish kept in these temperatures will need added oxygen to keep from being stressed.
In the case of Ulcers however, you should heat the system to 82 degrees, as this is the temperature the that specific ulcer causing bacteria will be killed.