Calculate stabilizer (CYA) levels to protect your chlorine from the sun. Optimize sanitization efficiency and prevent over-stabilization issues. Cyanuric acid acts as a sunscreen for your pool, preventing up to 90% of chlorine loss during hot, sunny days.
Measure your current Cyanuric Acid (CYA, also called stabilizer or conditioner) with a turbidity test, and have your pool volume ready. CYA shields free chlorine from UV sunlight, cutting daytime loss dramatically, but it also weakens chlorine's killing power, so the right level is a balance. Enter current CYA, target CYA, and volume. For traditional chlorine pools, 30-50 ppm is the common target; saltwater pools usually run higher, 60-80 ppm, because the generator replenishes chlorine continuously. The calculator raises CYA by dosing pure cyanuric acid (granular or liquid). It is important to know that stabilized chlorine products carry their own CYA: dichlor adds about 0.9 ppm CYA for every 1 ppm of free chlorine it delivers, and trichlor tablets add roughly 0.6 ppm CYA per ppm chlorine. If you sanitize with those, CYA creeps upward on its own and you rarely need to add more.
Method: granular cyanuric acid raises CYA about 1 ppm per 0.00813 lb per 1,000 gallons; in metric terms roughly 0.97 grams per 1,000 liters per ppm. Pounds = volume(gal) / 1000 x ppm_increase x 0.00813. Worked example: a 15,000 gal (56,800 L) pool reads 10 ppm and you target 40 ppm, a 30 ppm rise. 15,000 / 1000 x 30 x 0.00813 = 3.66 lb, about 58.5 oz (roughly 1660 g). Just as important is the FC:CYA ratio that governs sanitation: free chlorine should sit near 7.5% of CYA as a minimum, so at 40 ppm CYA you want roughly 3 ppm FC, and at 80 ppm CYA closer to 6 ppm FC. The calculator uses this ratio so your stabilizer choice and your chlorine target stay matched rather than fighting each other.
Accuracy matters because CYA is effectively permanent: it does not evaporate or burn off, so the only way to reduce it is draining and refilling with fresh water. Overshooting forces you to dilute, and very high CYA (above 100 ppm) causes 'chlorine lock,' where normal-looking chlorine readings can no longer kill algae and your shock target balloons. Granular CYA dissolves slowly, so the safest method is to place it in a sock or skimmer basket with the pump running, never broadcast onto plaster where it sits as acidic clumps and can etch the surface. Do not brush undissolved CYA across the floor. After dosing, wait 24-48 hours and circulate fully before retesting, since a too-early reading reads low and tempts you into a costly overdose. Recheck and adjust free chlorine to match the new CYA using the FC:CYA ratio.
Cyanuric acid (CYA), also called stabilizer or conditioner, acts as a sunscreen for your chlorine: without it, UV from the sun can destroy 75-90% of free chlorine within a couple of hours. A small CYA reserve lets the chlorine last through the day, so outdoor pools dose much more efficiently.
For a standard pool, 30-50 ppm is ideal. Saltwater pools usually perform best at slightly higher levels, between 60-80 ppm.
Add granular cyanuric acid by placing it in a sock or mesh bag and hanging it in front of a return jet, or in the skimmer with the pump running; squeeze it occasionally to help it dissolve. It dissolves slowly over a few days, so wait about a week before retesting. Never pour it straight onto the pool floor.
Cyanuric acid is very stable and does not dissipate. The only practical way to lower it is by draining and refilling a portion of the pool with fresh water.
If CYA is too high (usually above 100 ppm), it holds onto the chlorine too tightly, making it ineffective at killing algae even if your chlorine levels look normal.