Soda Ash SODIUM CARBONATE 25 lbs Bulk POOL SPA PH INCREASER TIE DYE + 100% Sodium Carbonate (aka Soda ash) Na2CO3. 25 lb bulk package of Soda Ash increase pH in swimming pool or spas ensure proper chemical bonding of the dye with cellulose (plant) fibers, typically before dyeing (for tie dyes) water softener in laundering