Most outdoor pools need cyanuric acid (stabilizer) to protect chlorine from UV degradation. Target 30-50 ppm for regular chlorine pools and 70-80 ppm for saltwater pools.
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Yes, most outdoor pools need cyanuric acid (also called stabilizer or conditioner) to prevent chlorine from being destroyed by the sun's UV rays. Without stabilizer, you'll burn through chlorine extremely quickly and struggle to maintain proper sanitization levels. Target 30-50 ppm for regular chlorine pools and 70-80 ppm for saltwater generator pools.
Cyanuric acid acts like sunscreen for your pool's chlorine. Without it, UV rays will destroy 75-90% of your free chlorine within just 2-3 hours of direct sunlight. This means you'd need to add chlorine multiple times daily, making pool maintenance extremely expensive and time-consuming.
However, cyanuric acid isn't just a simple additive - it fundamentally changes how chlorine works in your pool. As CYA levels increase, you need proportionally higher free chlorine levels to maintain the same sanitizing effectiveness. This relationship is captured in the FC/CYA ratio, which should stay between 7.5% minimum for maintenance.
All outdoor pools exposed to direct sunlight require stabilizer. Even pools with partial shade benefit significantly from CYA protection during peak sun hours. The only exception might be heavily shaded pools that receive less than 2-3 hours of direct sunlight daily.
Indoor pools typically don't need cyanuric acid since they're not exposed to UV rays. Adding CYA to indoor pools actually makes chlorine less effective without providing any protective benefit. Keep CYA at zero for indoor installations.
Saltwater pools especially need adequate stabilizer because the generator runs continuously, producing chlorine that would otherwise be rapidly destroyed by sunlight. These systems work best with CYA levels of 70-80 ppm.
CYA below 20 ppm provides minimal UV protection. You'll notice rapid chlorine loss and difficulty maintaining free chlorine levels during sunny days. Levels between 20-30 ppm offer some protection but aren't optimal for most situations.
CYA above 50 ppm (100 ppm for SWG) starts causing problems. High stabilizer levels make chlorine increasingly ineffective, requiring shock levels of free chlorine just for basic maintenance. Above 100 ppm, even shock treatments become insufficient for proper sanitization.
Use this formula: (Target CYA - Current CYA) × Pool Volume ÷ 3,000 = Pounds of stabilizer needed. For example, raising CYA from 0 to 40 ppm in a 15,000-gallon pool requires: (40-0) × 15,000 ÷ 3,000 = 200 pounds of stabilizer.
Important: Cyanuric acid dissolves extremely slowly, taking 24-72 hours to fully register on tests. Don't add more stabilizer until you've waited at least 48 hours and retested. Many pool owners overdose by adding more before the initial dose fully dissolves.
Test CYA levels monthly during swimming season using a Taylor K-2006 test kit or similar quality kit. Pool store test strips are notoriously inaccurate for stabilizer levels. When testing, ensure the sample has been circulating for at least 24 hours after any chemical additions.
If CYA exceeds recommended levels, your only options are dilution (partial drain and refill) or complete water replacement. There are no practical chemicals that remove stabilizer from pool water. Plan on replacing 1/3 of your pool water to reduce CYA by approximately 1/3.
This is why many pool professionals recommend using liquid chlorine instead of trichlor tablets - it provides sanitization without continuously raising stabilizer levels.
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