I also use iodized table salt (probably even has anti-clumping agent, but I'm not sure), no problems here either. I use it in my planted and unplanted tanks, tank s cories, loaches, and/or plecos, discus, guppies, everything you could probably think of....
Little late, but I will only use salt+heat for ich since I tried it on a juvie discus and he was free of the parasite within 1 day! Much, much faster than any ich medication that I've used in the past... much safer too

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The salt should also help out with the finrot. Though you may actually want to use the Q-tank for the sick fish so you can use more intensive methods, without subjected uninfected fish to everything. For fin rot, you may want to (slowly) go up to as much as 1 tbsp salt/ 1 g of water. I would also, however, go pick up an bacterial remedy from the LFS, such as maracyn, if the fin rot is more advanced.