At the hardware store they have a hose attachement made by Drain King that expands when pressure is applied. They use the device for cleaning out pipes so chemicals do not have to be used. Here is one for a 3"-4" pipe but I know they make one for 2" as well.

http://www.amazon.com/Water-Products...0?ie=UTF8&s=hi

Put this in the main drain outlet in the skimmer and see if you can back flush the blockage out of the drain.