You increase CYA by adding cyanuric acid, often sold as stabilizer or conditioner. CYA is available as a solid and as a liquid. The liquid costs a lot more, and generally isn't worth the extra expense. Solid stabilizer can take up to a week to fully register on the test, so don't retest your CYA level for a week after adding some. Solid stabilizer is best added by placing it in a sock in the skimmer basket. The pump should be run for 24 hours after adding solid stabilizer and you should avoid backwashing/cleaning the filter for a week.