Ich? (Fish experts, please!)?

What is the best way to treat ich? In my community tank, my small Columbian sharks have contracted it.They have the appropriate amount of salt in their tank, and so far I've added Super Ich Cure to the water twice (at half strength, since they're sensitive) and removed the filter cartridge to keep it from siphoning out the medication. They also have bacteria supplement in the water already. Before I started medicating they only have a few spots, but in those two days it's gotten much worse. They're very young, and I'm extremely worried. So far, none of the other fish seem to have it.