Ok, so one of my Plecos (Have 2) often has some weird color on him. He will be normal one day, then the morning next, he has patches of faded color on him, then in a few days, its back to normal. Its been off and on a while now, sometimes its got a reddish/orangish tint to it. The other Pleco maybe sometimes has a very slight fade in areas, but for the most part is fine. The other fish in the tank don't seem to have any problems. I havn't changed anything in the tank and do a 25% change once a week with a gravel cleaning. 55 Gal tank, one pleco is about 5 inches, the afflicted Pleco about 7 inches. What could be the cause? Thanks!