you could try adding more protein to the plecos diet.heres a evry short course on slimecoat and why plecos eat it -Anne
SLIMECOAT
Is a mucous created by the continal replacement of glandular cells know in the fishes skin hat produce a glycoprotein which is called mucin.Areas of the amazon where a number of plecos exist there is little in the line of protein based foods.Plecs are very adaptable to feeding on availiable food sources and one is the mucus coating of other fish,There is good
evidence of these fish doing this in the wild and plenty of evidence of these fish doing this in captivity. There It really would not be a suprise to find that mucus feeding is a common feeding method in many Loricariidae catfishes.