2 lbs (4 cups) at a time will add 5 ppm chlorine doses to your pool, and 4 ppm CYA doses. Just use the dichlor to add chlorine.

Power washers will definitely destroy cartridges. You don't need a special soap; the cartridge makers all recommend TSP. Full instructions here:
http://www.poolforum.com/pf2/showthr...ut-Damaging-It!