Hi dana, i dont have any experience with plecos' im sorry check the "
freshwater fish disease" or go to the species specific boards. the people we have here are just simply brilliant. help is not far away try to post the photo into your thread when you start a topic. there is a sticky to show you how. people here can work magic even more so with photos.
if you have washed your gravel and other "stuff" too much you may have washed your good bacteria away. they bacteria we need lie in the gravel and on the filter media its best to rinse your filter floss and other medias in used tank water! tap water has
chlorine and
chloramine. which is not good for the fish
test your water AMMONIA
pH NITRiTES and NITRaTES and post this on the disease board
good luck i will keep checking in on you
regards Dazzler