Pool shock works by rapidly raising chlorine levels to oxidize organic contaminants like sweat, sunscreen, and algae. It breaks down chloramines (combined chlorine) and restores free chlorine sanitization power.
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Pool shock works through a powerful oxidation process that rapidly raises your pool's chlorine level to eliminate organic contaminants and restore water clarity. When you shock your pool, you're essentially flooding the water with oxidizing chemicals that break down accumulated waste products like sweat, sunscreen, body oils, and organic debris that regular chlorine levels can't handle.
The key mechanism involves oxidation - a chemical reaction where shock treatments donate oxygen atoms to organic compounds, effectively breaking them down into harmless byproducts like carbon dioxide and water. This process also destroys chloramines (combined chlorine), which are responsible for that strong "chlorine" smell and eye irritation.
The most common pool shock contains 65-70% available chlorine. When dissolved in water, cal-hypo releases hypochlorous acid (HOCl), the active sanitizing form of chlorine. This type adds both chlorine and calcium to your pool, making it ideal for pools with low calcium hardness but problematic for those with high calcium levels.
Contains about 56% available chlorine and includes cyanuric acid (stabilizer). Dichlor dissolves quickly and won't affect pH as dramatically as cal-hypo. However, repeated use builds up CYA levels, which can eventually reduce chlorine effectiveness.
This oxidizer works differently than chlorine shocks. It oxidizes organic contaminants without adding chlorine, making it useful for routine oxidation without raising FC levels. However, it won't kill bacteria or algae like chlorine-based shocks.
When shock enters your pool water, several chemical reactions occur simultaneously:
Effective shocking requires reaching specific chlorine levels based on your pool's CYA (stabilizer) level. For pools with 30-50 ppm CYA, shock to 12-15 ppm FC. Pools with higher CYA need proportionally higher shock levels - use the FC/CYA chart to determine your target.
Dosing guidelines:
Always shock at dusk or night to prevent UV degradation of chlorine. Add shock directly to deep end with pump running for proper circulation. Never pre-dissolve cal-hypo in small containers as this can create dangerous chlorine gas.
Test FC levels 1 hour after shocking to verify target levels were reached. Continue testing every 2-4 hours during SLAM procedures until overnight FC loss is less than 1 ppm.
Regular shocking prevents problems, but certain conditions require immediate shock treatment:
Cal-hypo shock raises pH significantly, often requiring muriatic acid addition afterward. Add acid slowly - approximately 1 quart per 10,000 gallons to lower pH by 0.2 units. Always retest and adjust pH to 7.4-7.6 range within 24 hours of shocking.
Never mix different shock types as this can create dangerous chemical reactions. Store shock products in cool, dry locations away from other pool chemicals. Always add shock to water, never water to shock, to prevent violent reactions.
Wait until FC drops below 4 ppm before swimming, typically 8-24 hours depending on CYA levels and shock amount used.
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