I use Kordon Rid-Ich plus, and it works great. Slowly up the temp to 29C (82-84F) and dose per what the bottle says. Heating the tank speeds up the life cycle of the parasite, and allows the medication to kill it, as the meds are only affective on the free swimming parasites. about a week of treatment and your fish should be okay, maybe up to two weeks.
I would suggest salting the tank so the fish can breathe, but that may be hard on the pleco. So don't do that unless someone who knows for sure can clarify.