It really depends on the individual pleco. I've got one in my 29gal tank w/my yellow labs. When I got him, I was having to scrape down the glass every couple of days. Couldn't figure out why so much algae, nitrates were low, only thing I could figure out was the tank was getting too much sunlight. So anyway, I decided to get a small pleco and waited to see what would happen. Good lord, in 2 days my 1.5inch bulldog pleco had eaten every bit of alage in my tank. He even hoovered the sand.

. I've had him for about 1 1/2 months now and I see him every day chomping on non existent algae on the glass. He's even cleaned all of my rocks, so I don't get to have that natural look.
