I agree with the previous post that loaches are more susceptible to ich because they are scaleless but this also means they are more sensitive to the medication. Do not use a full dose with these. I have seen them survive through full doses but sometimes the medication can be what kills them. This is the reason that I look at my fish tank almost daily and check every fish to see how they are doing. If you can catch ich fast enough you can usually treat it with simple water changes, aquarium salt and a stress coat. I've even bought oscars that had ich in the store and I treated them with just salt when I got home. Within 2 days, they had no more white spots and it hadn't spread to my other fish. Raising the temperature is always good as well because it speeds up the life cycle of the ich parasite. This allows the medication to have a stronger impact on the tomitic stage (when it is susceptible to the medication) of Ich. THe downfall of raising temperature though is that elements such as Ammonia and Nitrite are a lot more lethal at higher temps. If the water quality isn't great and you raise the temp, you may have the opposite effect that you wanted!
Extreme cases of Ich often lead to secondary fungal and bacterial infections too so sometimes multiple treatments are needed (but never at the same time).