Get thee to the grocery store and buy a zucchini stat. Cut it n half lengthwise and de-seed it, attach a 4" long chunk of it to a piece of rigid airline tubing or rubberband it to a fork, whatever, and get it in there. Some will tell you to blanch the zucchini first to help make it softer. I don't do that. In the meantime, either get yourself some Kordon "Rid Fungus" or other fungus cure. I recommend the Kordon product because it can be used in your main tank without harming animals. It will also take care of ich if you have it. Algae wafers aren't enough for plecos, especially if you have no driftwood (you need driftwood for plecos) or a tank without enough veggies and/or algae to eat. Plecos are pigs. They will eat constantly, and are poop machines.
i am apprehensive about using some of the meds with plecos. Plecos, algae eating varieties anyhow, have extra long guts with specialized bacteria to process the veg/cellulose/etc that they graze on. Using an anti-fungal with antibiotics in it kills the beneficial bacteria which allows them to process and get nutrition from their foods.
If it were my fish, I would probably start by fattening it up, doing daily water changes, and probably pull it frmo the tank and topically treat the spot (since it is one spot).]
That's why I recommended that Kordon product. It's unique in that it doesn't disrupt bacteria. It's an herbal product. If akagorilla wanted to call Kordon and talk to the Dr. there I would encourage it. Spot treating is also a good idea.
In the future, a quarantine tank for new fish can save you lots of headaches. Even a rubbermaid bin can work for the duration of quarnatine. QT tanks are cheaper and easier to treat, and make it so the rest of your livestock is safe from illness, as well as plants which can be sensitive to some meds as well.