someones gonna say this, so i'll say it, if its a common pleco, it gets to a foot, or larger i believe, and a 29 gallon is too small for it. if its a chinese algae eater, that gets to be around 6 inches i believe, and with convicts which get to be around 8 inches i think, thats a whole lotta fish (correct me if im wrong on this)
It would depend on what kind of pleco. You can look here and look for some that don't get huge http://planetcatfish.com I think that would be a good size for the convicts though.