So far I have no other ideas.
IMO, it is unnecessary to raise the temp right away when treating with salt and it is very rarely necessary to raise the temp that high ever, almost never above 84-85 F.
If 3-4 days of salt (no temp) treatment show no effect, then the temp can be bumped up little by little. The higher the temp, the more aeration/agitation will be needed as the tank water will lose much oxygen.
Salt needs to be added step-by-step too, perhaps over 3 days, from 1 table spoon a gal, to 2, then to 3.