I would bet the pleco stripped the slime coat off it. This opened it up to infection. The slime coat protects the fish it's like having your skin peeled off. The red streaks sounds like septicimia an infection of the blood. My suggestion would be to seperate the two fish. As far as treatment goes, try using API Triple Sulfa and salt dosed at 1 tablespoon per ten gallons of water. The salt will help regenerate the slime coat while the 3x sulfa will fight the secondary infection. I like 3x sulfa in a higher Ph as it is generally more effective but should still work here reasonably well. Discontinue all the Pima/melafix oil based things like this IMO interfere with resperation and prevent adaquate transfer oxigen by coating the gills. MY .02 on that stuff. Kanamycin can be combined with 3x sulfa but may not be necessary so don't rush into it yet but it is great to have on hand. Get the 3x, seperate the fish and treat as I discribed. You have to get the bichir away from the pleco they are like ottos sucking the slime off discus if you've ever seen that once ottos get a taste for Discus slime you can't stop them, they are like remoras on them.