I talked to a tech support person at one of the big chemical companies and he said the following:

Trichlor tablets are about 54% CYA.

One pound of anything dissolved in 10,000 gallons of water will yield 12ppm.

Therefore, one pound of trichlor in 10,000 gallons adds about 6.5ppm CYA.

Each 3" puck weights 8 ounces, so if you use two a week that's adding 6.5ppm per week per 10,000 gallons.

Soooo...

If I have a 15,000 gallon pool and add two pucks per week, that's (10/15)*6.5 = 4.3ppm

Is that right?

TW