From what I gather here, they will... but depending on how big the outbreak is, they might not get to it all. Correct me if I'm wrong, but I would definately clean it off the glass, but make sure you don't irritate the sand too much since the algea will spread.
Cut down on how long you have your lights on, and do a small water change with RO
water from a LFS
. If you have a small air tubing line, use the hose to lightly syphon (sp?) off the top of the sand's surface while you take out your water for the change. I learned that tap water will only lead to problems down the road (especially if your tap water is bad). Some people I hear do not use it, and I myself didn't use RO
water when I had my tank, and I had similar problems that never really went away. Cooincidence? Probably not... at least with me. Not sure if you can afford an ro
unit, but I would at least suggest to get RO
water and go from there. Cheers