Amazon offers the Arm & Hammer Clear Balance Pool Maintenance Tablets 16-Count Tub for $19.97. Add it to your cart via Subscribe & Save to cut it to $18.97 and bag free shipping. (Walmart charges a buck more via pickup.) That's the lowest total price we could find for this quantity by $9.

Be sure to cancel Subscribe & Save after your item ships to avoid being billed for subsequent shipments.