I have a Clown pleco, he eats green algae, don't know about brown algae, but they only get to be about 4 inches as compared to standard plecos who get about 12 inches.
doesn't read like you really care....I say buy your pleco which you seem to want anyways. If it doesn't clean up your algae (which I don't think they do well for long) you'll end up cleaning it yourself. But you'll have the fish you seem to really want. As the owner that is the bottom line.
Most plecos will eat algae when they are small as a juvenile, but once they get bigger they dont feed on it as much. As such they are NOT the best algae eaters. If you truly want an algae eater go with otos, or maybe a snail...
If youre just set on getting a pleco, then try the bristlenose they are said to be one of the better plecos for algae, though I dont have direct experience with them. The goby pleco or pitbull as its some times referred to as is not a primary algae eater. I think they do however only get up to about 2-3" so they might be a good fit as a plec in your 20g.
FINALLY, THANK YOU!!! For the record, I appreciate the extra advice from everyone else, but I was asking a specific question by the end. Thanks, legendaryfrog!
I have brown Alge on a rock and my Stick pleco and "regular"LFS pleco can't touch it. I will go to the LFS that has a larger variety.
Thanks for the help!
This sit is really helping me!