they are not only a sign of overfeeding. they can show a slack maintenance schedule, no disrespect intended. vac the gravel that bit more and up the waterchanges a bit to twice a week if you already do it once a week. if you only feed every couple of days then i doubt its the amount of food as long as they eat it all. but from what i understand P's are quite messy and debris from them eating will sink and sit on/in the sand/gravel.
so again back to gravel vac.