Garlic does not get rid of ICK. The only way to get rid of ICK is to treat with a copper medication, or no fish in tank.
To treat a fish with ICK you will need to treat with copper medication, or hypo.
Now that I said that. I have ICK in my tank. My Hippo tang was almost all white dew to ICK, and my Japanese tang had it bad as well. Not wanting to set-up a QT tank I tried some reef safe medication. (don't wast your money on that junk). It did nothing, I tried 2 different brands.
I then read about garlic here on RC, so I gave it a try. With-in one week 98% of the ICK was gone. At first I just thought it was just in the reproduction stage, but here I am 3 months later and still just a small trace of ICK.
So no, it will not kill or get rid of it, but it will keep it under control. Some say it dew to it makes fish eat more, but my fish never lost there appetite. My fish would always go nuts over the food before & after.
I personally think it helps there immune systems but there are no studies to prove it.