Pool shocking involves introducing a concentrated dose of sanitizing chemicals to pool water, typically chlorine or a non-chlorine oxidizer. This process serves to sanitize and clarify the water by breaking down contaminants that accumulate over time. It helps maintain a clean and inviting swimming environment.
Understanding Pool Shocking
Pool shocking, often referred to as superchlorination, is a maintenance practice designed to rapidly increase the level of sanitizing agents in the water. This elevated chemical concentration works to oxidize chloramines, which are formed when chlorine reacts with nitrogen-containing compounds like sweat, oils, and urine. Chloramines reduce chlorine’s effectiveness and can cause a strong chemical odor.
Various types of pool shock are available, each with distinct chemical compositions and applications. Calcium hypochlorite (cal-hypo) is a common and economical choice, effective against algae and bacteria, though it can increase pH levels and requires evening application to prevent UV degradation. Sodium dichlor is a stabilized granular shock containing cyanuric acid, which protects chlorine from sunlight, and has a nearly neutral pH. Potassium monopersulfate (MPS) is a non-chlorine, oxygen-based shock that oxidizes contaminants and allows swimming within minutes of application, without affecting chlorine levels or leaving residues.
Indicators and Consequences of Excessive Shock
Adding too much shock can lead to an over-shocked condition where chemical levels become excessively high. A primary indicator is an extremely high chlorine level, often exceeding the safe range of 1-3 parts per million (ppm). The water may also appear cloudy or discolored, and a strong chemical odor, often mistaken for chlorine, is actually due to chloramines or other byproducts. Swimmers may experience skin, eye, and respiratory irritation, such as dryness, itchiness, redness, and coughing, if exposed to highly chlorinated water.
Beyond immediate discomfort, excessive shock has several negative consequences. High chlorine levels can upset the overall chemical balance of the pool, particularly by lowering the pH, making the water more acidic. This increased acidity can lead to damage to pool surfaces, such as etching or discoloration of plaster, concrete, or vinyl liners. Pool equipment, including pumps, heaters, and filters, can also suffer corrosion and premature wear. In severe cases, the off-gassing of chlorine can create a health hazard, causing respiratory distress, especially for individuals with conditions like asthma.
Restoring an Over-Shocked Pool
If a pool is over-shocked, immediately cease all chemical additions, including any automatic chlorinators or floating chlorine dispensers. Allowing the pool to remain uncovered and exposed to sunlight is an effective, natural method for reducing elevated chlorine levels, as ultraviolet (UV) light helps break down chlorine. This process can take several days.
For a more rapid reduction in chlorine, a chemical neutralizer, such as sodium thiosulfate, can be employed. This granular product quickly reacts with and removes free chlorine from the water. It is important to follow the manufacturer’s instructions carefully for proper dosage, as overuse can lead to an excessive reduction in chlorine and potentially affect pH levels.
Partial draining and refilling the pool with fresh water is another method to reduce high chlorine levels. This dilution technique is particularly useful for extremely high chlorine concentrations, though it can also impact other chemical balances in the pool, such as pH and alkalinity. After any corrective measures, re-test the pool water to ensure chlorine levels return to the recommended range of 1-3 ppm before allowing swimming.
Preventing Over Shocking
Preventing over-shocking requires consistent and accurate water testing. Reliable test kits or strips allow monitoring of chlorine, pH, and other chemical levels regularly, ideally weekly during swimming season. Knowing the pool’s current chemical status helps determine if shocking is necessary and how much to apply.
Calculating the correct shock dosage based on pool volume and water conditions is crucial. Most products provide dosage instructions, often recommending one pound per 10,000 gallons for routine maintenance. Adhering to manufacturer guidelines prevents adding too much chemical.
Shocking the pool in the evening allows the product to work effectively overnight without immediate degradation from sunlight. This timing allows chemicals to dissipate before the pool is used. A prudent approach is to “start low and go slow” with chemical additions, allowing time for the shock to circulate before adding more.