Straight out of Pool School:
CYA - Cyanuric Acid
CYA can be raised with cyanuric acid. Cyanuric acid is sold under a variety of names, including Stabilizer, Conditioner, Instant Pool Water Conditioner, Stabilizer 100, Stabilizer & Conditioner, etc. Instant Pool Water Conditioner is a liquid product which is significantly more expensive than the other forms.
Solid/granular cyanuric acid (CYA) should be placed in a sock and the sock put in the skimmer basket or suspended in front of a pool return. After adding CYA you should leave the pump running for 24 hours and not backwash/clean the filter for a week. Squeezing the sock periodically will help it to dissolve faster. Test and dose chemicals in your pool assuming the amount of CYA added is in the pool according to Poolmath. CYA can be tested the day after it is fully dissolved from the sock.