don't worry about catching him, use garlic to treat the ich.. won't harm anything else in the tank. You can use the garlic extreme from Kent I believe, but when I had my hippo tang (those things get ich if you look at them the wrong way) I used to use a teaspoon of juice from minced garlic in a 55 gallon setup.. it increases the appetite of the fish and they are able to fight it off naturally. I did that once every other day until the ich went away...
catching them... I usually end up pulling all the rock out of the tank and catching them without anywhere to hide... in a 55 it's a pia.. can't imagine doing that in anything bigger...