If the pucks are 3" 8-ounce (some weigh less), then for a 13,500 gallon pool, 12 pucks will get you about 30 ppm CYA while 20 pucks will get you around 50 ppm CYA.

The general rule is that for every 10 ppm Free Chlorine (FC) added by Trichlor, it increases Cyanuric Acid (CYA) by 6 ppm. This rule is independent of concentration of product or size of pool.

Richard