It really depends on what kind of algae you have, and why. High phophates can be from using tap water, as can silica. If this is the case, then yes, RO will get rid of it eventually. If the algae is from too many nutrients, RO won't help a bit. Reduced feedings will. If the algae is from light bulbs that are old and have shifted spectrum, new bulbs will help. If you have the red slime algae (that's actually bacteria, not a true algae), RO may help, but probably isn't a sure thing.
In my experience, it's usually not just one thing that causes an algae problem. It's a combination of several things. This is a starting point.
We have a lawn mower blenny, and he eats a lot of algae off the glass. Because we don't mind the natural look of some algae on the rocks and back walls of the tank, it's no big deal. If we were trying to get rid of the algae completely, the blenny would be a silly waste. As is, it's fun to watch him 'kiss' the glass and scrape the algae off. Leaves weird little tracks through the algae, like some sort of bizarre crop circle.
