All good comments with special emphasis on the CUC(snails).
It's not necessary or even advisable to remove rock from the water. LR has many tiny holes which are home to all kinds of bacteria, bugs and worms. Because of the surface properties of water and air, as LR is moved water drains out air fills the tiny holes and pores. This air actually resists water from re-entering the holes. It can take weeks or even months for the water to again fill those tiny holes. What does air do to the bacteria, bugs and worms? That's right, it kills them, so to avoid the death and subsequent pollution/Nitrogen Cycle we should do all we can to eliminate or at least limit exposure to air.
The pollution that comes from exposing rock to air can actually thwart all the time and trouble that went into manually cleaning the rock before submerging it in the new tank. This new source of pollution can cause the algae to grow back with a vengence, even if all visible algae was removed and the LR was dipped in a Hydrogen Peroxide solution. In my thread about setting up an affordable reef aquarium, I describe the best way to move rock from one tank to another.
http://www.utahreefs.com/forum/forum_posts.asp?TID=9244
Regarding what would be best way to rid the rock of algae in your circumstance, my suggestions depend on how it looks right now. Can you describe it or even better, post a pic of the tank with some closer shots of the rocks with algae? Also, are Alkalinity and Calcium within the preferred range? (Alk 8-14 dKH and Ca 350-450ppm)
Edited by Mark Peterson - January 05 2010 at 9:27am