Take the ich meds back to walmart and don't dose the tank at all . . . ESPECIALLY with the Pleco in there.
Slowly turn up the heat in the tank (about a degree per hour) until just ABOVE 86 degrees, then leave it there for two weeks after all signs of ich are gone. That's all you need to do to cure ich.
The ich meds WILL kill your pleco, even if you halve the dose like it says on the bottle.
Believe me, I learned the hard way. Take that stuff back. Raising the temp is all you need.
Also, when the ich is in its state that it is visible on the fish, the ich meds are virtually useless anyway. That stuff is only effective for a very short period of time when the parasite has left the fish and moved to the substrate before it goes in search of another host. Catching it during that time is, at best, a crapshoot.