How much stabilizer?
Outdoor chlorine pools usually run 30–50 ppm CYA; salt-water pools often 60–80 ppm because the cell produces chlorine continuously; indoor pools and hot tubs need little or none. Remember that higher CYA means you need more free chlorine for the same sanitizing power (see the chlorine calculator).
Adding it
Granular cyanuric acid dissolves slowly — often several days. Put it in a sock or mesh bag in the skimmer basket or in front of a return, and don’t backwash for a few days. Retest a week later before adding more. Liquid (slurry) stabilizers act faster.
Too much CYA
The only reliable way down is replacing water. Products that claim to remove CYA exist but are expensive and inconsistent.
Not professional advice. Results are estimates for residential pools and hot tubs. Read and follow product labels: add chemicals separately, to water (never water to chemicals), with the pump running, and retest before adding more. Commercial and public pools must follow local health codes.