50%WC, Raise the temperature to 85°, add some non iodine salt.1tsp/10gal, wait 24hrs, 50%WC & keep this schedule until the itch is gone.
Unless you're using a crappy brand of table salt, the anti-caking agent is unlikely to be harmful to your fish. The most commonly sold salt (Morton's) uses calcium silicate as an anti-caking agent. Calcium silicate is essentially a combination of limestone and diatomaceous earth. Diatomaceous earth is not harmful to fish, and is actually used in a diatom filter, which will get just about everything out of your water (excellent water polisher).
Furthermore, iodine is a necessary staple in a fish diet, and many fish foods contain it. Also, the amount of iodine in salt is so negligible, you would pickle the fish before you would have a toxic level of iodine in the water.
"Aquarium salt" is made from evaporated seawater. Which means it's not pure salt, and you don't know what you're getting with it as far as other minerals, and in what concentrations.
If you are going to raise your water temp up to 85 degrees, do it slowly! Be aware that by raising the temperature, you're reducing the amount of oxygen in the water, so you may want to add an airstone.
Here is a pretty good article on cichlid-forum.com breaking down some of the different treatments for ich:
http://www.cichlid-forum.com/articles/ich.php
