no, no, don't clean off the algea. Otocinclus' are amazing fish and are my favourite fish for maintanance. First, do you know what kind of algea it is (horse hair, soft stuff that you can wipe off with your fingers, green spots that area extremely hard to get off? What kind of lighting do you have with your tank-fourlessent, incandessent? Fourlessent lighting can make algea grow extremely fast... I found that if I had 'soft algea' the oto's would do an amazing job of eating it up. For more 'exotc' algea like red or horse hare the sae's are the way to go-but I found them doing a lousy job at eating the 'soft algea'. As for the 'hard green spots that are hard to ge off' I have not yet found a fish that would eat it. I have to get out my scrub brush and 'scrape' it off. (difficult work)
Ok, I hope this helps, bon chance!