I love my clown plecos. In fact, I'm not 100% sure of what they eat, but I've two in my 20H and have not had algae. I don't have any CAEs, SAEs, Ottos or anything else that is an authentic algae eater. My Rainbow Shark might help prevent algae growth because he seems to enjoy eating the protien stuff that coats the surface of the decor. The two clown plecos seem to love Hikari bottom feeder waffers, Wardly Spirulina chips, Hikari Carnivor waffers, Tetramin bottom feeder tabs, and are pretty omnivorous from what I've been able to tell. I don't the exact L-species I have, but they came in as clowns *shrug*.
Algae prevention should not be left up to just the fish though. Proper light and nutrient mangement in the first place goes a much longer way to keeping a tank algae free.
~~Colesea