Does anyone know/understand how the "poolcalculator" figures out TA concentrations? I am having trouble duplicating the TA result generated by the poolcalculator. Given a volume of 20,000 gallons (US) and 0 ppm TA, the calculator generates a result of 563 oz (35 lb) of baking soda required to reach 120 ppm. However, (35 lb) / (20,000 gal x 8.35 lb/gal) x 1,000,000 = 210 ppm. Does anyone know how the calculator arrives at 120 ppm?