unfortunately ID sharks are known to be susceptible to Ich, and die from it, this is the reason why I do not have any ID sharks, after 3 attempts and a different type of Ich treatment every time they still died on me. my suggestion is massive water movement, lots of air is also good. I have noticed that they tried to swim in the bubbles as much as possible when they had the ich, I was also increasing the temperature to 90 degrees and they tolerated it... but nonetheless they spots increased on their bodies and every time they died.
sorry for the downer, hope they make it for you, keep us updated.