Ich can definitely kill your fish and all fish, especially saltwater species should be quarantined before placing them into the main tank. There are lots of fish meds at the store for treating ich. I've used rid-ich+ and it works well. I dose everyday with 20% water changes daily while the fish are in
QT. Once they show signs of ich I'll leave them in qt for a further 4 weeks or so while treating them.
You have to turn off the protein skimmer when using medications otherwise it just gets skimmed out of the water. I'd try to get them into a
Quarantine Tank asap and treat them in qt if you have a setup with
live rock or inverts in your main tank. The meds could harm the rock and inverts.
Hope that helps,
Mike