What medication is best? I've read about adding rock salt to the aquarium, but it already has aquarium salt (1 tbs/ 5 gallons). Is that too much salt? There are also platies, ghost shrimp, and coto catfish in the tank.
I use the salt method and it has never failed. The thing is to bring the salinity way up and increase the heat. The heat speeds up the life cycle of ICH and the salt kills it. Since you use salt allready the ICH in your tank may have a little more tolerance then most strains. There have been people that said this treatment doesn't work because their strain of ICH withstood it. It has always worked for me , when I did it per directions in this article. It may be that the people using the salt method did it incorrectly or didn't bring the levels up for as long as necessary. I like to stay away from the more harsh medications because they can usually cause other problems. I also would reccomend not using rock salt unless it is food grade. Most rock salt for melting ice is very dirty. You should probably isolate your betta to a QT/hospital tank while treating him.The cats most likely wont like the salt and if you do have to use a stronger medication its better to only treat the infected fish.
Here is a link that might be useful: treating ICH with salt