I got rid of mine for that exact reason. Every morning thank bottom was covered in pleco spaghetti poo. Absolutely hated it. I also found that they really didn't seem to eat all that much algae.
It's a shame because I am a fan of plecos I just don't like their mess.
I feel that there are better methods of algae control with less mess. When my tank was planted my nerites and otos did a great job. I still have a few in my hard scape now