To raise cyanuric acid (CYA) in your hot tub, you'll need to add a stabilizer product, typically granular cyanuric acid. Dissolve the recommended amount in a bucket of hot water first, then slowly pour it into the hot tub while the jets are running to ensure even distribution.
No, you should not add cyanuric acid every time you add chlorine to your hot tub. CYA does not get consumed like chlorine; it only leaves the water through dilution or draining. You only need to add CYA when your test results show that the levels are below the recommended range. Over-adding can quickly lead to excessively high levels and chlorine lock.