How to Shock Your Pool: Everything You Need to Know

Fighting a green, hazy pool? Shocking a pool is the best method of removing algae and cloudiness. That glistening pool is within steps from your fingertips. But how to shock a pool to achieve it? Keep on reading!

Pool shock generally refers to the addition of specific chemicals in a certain amount to the pool water to increase the level of chlorine. Adding a chlorine-based product or a non-chlorine oxidizer instantly destroys bacteria, algae, and other contaminants. It's a powerful, focused disinfection to assist in keeping a healthy and clean pool environment. Therefore, shocking is a critical part of your pool maintenance to turn it from green to blue. 

What exactly is Pool Shock?

One of the common methods of chlorine-based pool shock is superchlorination. It deliberately raises the free chlorine (FC) levels, often 5-10 times the normal FC. It is like a periodic deep clean or oxidizing water treatment for the pool to restore the water's health and destroy microorganisms.

So, is shock the same as chlorine? Not really. Shocking uses a concentrated chlorine dose as well as non-chlorine oxidizers. In contrast to regular chlorination, a significant dose of chlorine powder or liquid in shocking works faster than chlorine tablets in stopping unwanted organic growth. 

Shocking a pool gives a deeper and more sanitary clean than routine pool upkeep. Here is why high levels of free chlorine matter:

• To kill bacteria, algae and chloramines (a byproduct of chlorine with nitrogen)
• To avoid the buildup of microbes and disease-causing agents
• To enhance water quality
• To keep water from going cloudy or green
• To eliminate the possibility of eye, skin, and respiratory irritation

Five Steps to Shock Your Pool

Whether you have an in-ground or above-ground swimming pool, super chlorinating a pool is easier than you thought. Remember to handle the concentrated chlorine with safety precautions.

Step 1: Pre-Shock Preparation

Firstly, gather all your supplies like protective eyewear, chemical-resistant gloves, closed-toe boots, a liquid testing kit, a stirring stick, shock and a bucket (to pre-dissolve). Test the pool water by checking the levels of free chlorine (FC) and combined chlorine (CC). Adjust the pH to 7.2-7.4 and alkalinity between 100-150 parts per million (ppm) for optimal shock effectiveness. 

Step 2: Calculate Your Shock Dosage

How much chlorine you need for shocking depends on the pool's volume, shock agent, current chlorine levels and the presence of algae. Read the shock product label for dosage instructions.

Step 3: Add the Shock

After turning on the pump, add the pre-mixed shock solution to a five-gallon bucket. Pour evenly near the corners to prevent bleaching of vinyl liners of pools. If using granular shock, always add shock to water, not water to shock. 

Step 4: Wait For Circulation

Allow the circulation by running the pump for 6-8 hours at least or overnight. It will ensure thorough distribution and filtration. 

Step 5: Retest Pool Water

Before jumping into the pool, wait for free chlorine to drop to 1-3 ppm. Retest FC and pH levels using strips or a kit. If the water has a strong chlorine odour, it signals poorly treated water. If chlorine reduces to 0 ppm, you may need to re-shock the pool by raising FC until CC is 0.5 ppm. 

When to Shock Your Pool

Generally, you should perform a pool shock every two weeks or so during the swimming season. The frequency will depend on the following indicators:

• Visible algae formation
• Cloudy water
• Free chlorine levels reach zero
• Strong chlorine smell due to chloramines or CC above 0.5 ppm

However, if your FC, pH, and stabilizer (CYA) are kept in the recommended ranges and you regularly adjust your water, routine weekly shocking is considered unnecessary.

There are some occasions when water is more susceptible to contamination and requires a shock:

• On the first and last day of the swim season
• After pool parties 
• Following extreme rainfall and strong winds
• During hot spells
• At night, to minimize UV degradation of the unstabilized shock

Choosing the Right Pool Shock

The type of shock matters as some shocks affect pH and CYA levels. There are 2 types of shocks.

1. Chlorine-Based (Adds Chlorine To Pool)

• Calcium Hypochlorite ("Cal-Hypo" ): It is an unstabilized shock in powder or tablet form that is strong enough to kill algae by raising pH. But it increases calcium hardness (chances of scaling) and degrades in sunlight.
• Sodium Dichlor: It is a stabilized shock powder that dissolves relatively quickly and keeps the pH neutral. It contains cyanuric acid (CYA), and excessive CYA levels (over 70–80 ppm) may lead to "chlorine lock."
• Sodium Hypochlorite (Bleach): It is a liquid and unstabilized shock that is less concentrated than powder shocks and is best for green pools. It does not add CYA but tends to increase the pool's pH, thus requiring a pH reducer like muriatic acid or sodium bisulphate

2. Non-Chlorine-Based (Oxidizers)

• Potassium Monopersulfate (MPS): It is a granular shock that oxidizes organic contaminants without adding chlorine. Although it sanitizes any sweat, oil, dead skin or urine (chloramines) effectively, it does not kill excessive algae or bacteria. The plus point? It does not affect CYA levels.

Pool owners must maintain proper water chemistry and sanitation levels as sometimes shocking would still cause algae to grow due to insufficient CYA or the wrong shock type. Relying solely on stabilized chlorine tablets can increase CYA levels and reduce chlorine's effectiveness. If the algae-free water is still cloudy, add a flocculant to accumulate particles. 

Conclusion

During heavy usage, the free chlorine levels deplete considerably. To bring it back to normal levels, make sure to perform a pool shock. It is important for maintaining the water quality as well as providing a safe swimming environment. 

Once the shock has removed contaminants and killed algae, those particles tend to fall to the bottom of the pool. Rather than vacuuming by hand, send in your robotic pool cleaner. It will take this particulate sediment and dead organic material, leaving your pool sparkling and welcoming. It's the ideal icing on the cake for your shocking process.