They will contribute a lot of waste when you first put them in the tank because there is usually so much algae for them to eat right off the bat since there was not a pleco in there to start with. Once they clean it all up then they aren't quite as bad as people make them out to be far as being waste machine.
I'd have to disagree - even if they eat all the algae in the tank then they still need food... unless you're talking about not feeding them.
You're missing my point, I would never suggest not feeding a fish you know me better than that. I feed my plecos daily, but if you have a tank that has been without any plecos in it for a long time then when you first put one/some in it they have an
overabundance of food (lots of algae) that they will tear through until it is all gone. So they will produce more waste when you first put them in the tank until they clean up all the algae. After that they don't seem to produce as much waste once you get them on a normal diet of wafers/pellets and once a week zucchini.
When I first got plecos I had about 8 months of algae growth on the 3D background of one of my 55g tanks. The waste they produced the first week was unreal while they were cleaning it up. After that it tapered off and was not bad at all.
Think of it this way. Put a fat kid in a room full of cake and what's he gonna do? Eat himself into diabetes until all the cake it gone. Then you put him on a regimented program of one piece of cake per day for his normal food after that
