1 - 1 1/2 tsp salt per gallon, turn up water so it NEVER drops below 86 degrees. I shoot for 88 degrees - Clowns don't mind heat. If you are prone to over stocking or have little surface agitation, add an airstone to keep oxygen levels high. After no sign of white spots, maintain treatment for another 7 days. I usually do water changes/full gravel vac every day until 1 day after no sign of white spots. As for salt - table salt - iodized or not - it doesn't matter - works fine. It should be sodium chloride, not some other kind of salt. (you could use marine salt if you have the bucks I guess)
My pod of clown loaches is over 10 years old. Have prescribed this treatment to countless others with great success. Hope this helps.
As for temp resistant strains of ich... if the water EVER drops below 86 degrees, it gives the killable stage a chance to survive and find a host. Hence, I shoot for 88 to allow for inaccurate thermometers.
I use this on all my fish - for corys I only use 1 tsp/gal salt per gallon. For central americans cichlids, heck, rub them down with salt and broil them, they'll probably survive! (if they don't, bon appetit!)