SODIUM CARBONATE - Soda Ash 5 lbs Bulk Fast Shipping Pool Tie dye 5 lb bulk package of Soda Ash 100% Sodium Carbonate (aka Soda ash) Na2CO3. 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