Along with the Nature II cartridge, this is the staple product to keep your Softub crystal clear. With average use cycles, a small amount added (1/4 oz.) midweek, and larger shock on weekend (3/4 – 1 oz.) keeps everbody happy. Powdered dichlor, available chlorine = 55% Contains 99% Dichloro-s-Triazinetrione Dihydrate.