ich is a parasite. when it's visable on the fish it isn't vulnurable to medication or sterilizer. however, in some part of its life cycle, it detaches. i would think that, then, it would be killed by the sterilizer. mayble not. even if it doesn't kill the ich, which i don't know why it wouldn't, a sterilizer will destroy other free floating pathogenic bacteria, viruses, or parasites which will keep your fish healthier. thus the fish will be less likely to get any kind of sick, even ich.