For every 10ppm of Free Chlorine the pucks add, they will add 6ppm of CYA. Be sure to watch your pH as well, as pucks are EXTREMELY acidic. I'd spend $10 and buy a floater for the pucks rather than put them in the skimmer, where they can clog the system and wash components with a lot of acid if the pump is off.

Be patient when adding CYA.