Depending on your pool usage and weather conditions, you should be shocking your pool at least once a week – or at least every two weeks – to maintain healthy water and prevent algae growth. But as straightforward as it sounds, pool shocking is actually a delicate process. 

Choosing the wrong pool shock can disrupt your water chemistry and even damage your pool equipment. For instance, too strong chemicals might harm your pool’s filter, while mismatched products could leave your pool inadequately sanitized. 

To avoid these issues, it’s important for you to select a shock that aligns with your pool’s needs and condition

Understand the Types of Pool Shock and Their Uses

Pool shocks aren’t one-size-fits-all. Cal-hypo, dichlor, and non-chlorine shocks each serve distinct purposes.  So it gets down to issues you’re addressing – like algae growth, cloudy water, or routine maintenance – and your pool’s unique setup, including sunlight exposure and chemical balance.

Cal-hypo Shock:

Calcium hypochlorite (cal-hypo) is one of the most powerful and fast-acting pool shocks, with a high free available chlorine (FAC) content of 65–75%. This makes it highly effective for tackling bacteria, algae, and other contaminants. However, because it’s unstabilized (lacking cyanuric acid), it’s vulnerable to sunlight degradation. To maximize its efficiency, cal-hypo should always be added at dusk or nighttime, allowing it to work uninterrupted for 8 hours without UV interference.

Cal-hypo is ideal for performing “breakpoint chlorination,” where chlorine levels are raised to 10–12 ppm. This process eliminates chloramines, restores sanitization, and prevents future water quality issues. However, due to its potency, it’s best reserved for addressing severe pool problems, like algae blooms or high contaminant loads, rather than routine maintenance.

Dichlor Shock

Sodium dichlor shock is a stabilized alternative containing 50 – 60% free chlorine, making it a dependable option for daytime use. Its built-in cyanuric acid (CYA) protects chlorine from UV degradation, ensuring prolonged sanitizing action. However, this stabilization has a trade-off: for every 1 ppm increase in free chlorine, dichlor adds approximately 0.9 ppm of CYA, which can lead to elevated CYA levels over time.

On the plus side, dichlor shock dissolves rapidly, thanks to its sodium content. This minimizes the risk of bleaching pool liners or damaging surfaces, making it a gentler option compared to cal-hypo.

While it is less aggressive than cal-hypo at eliminating algae, it’s still effective for maintaining water quality in pools with heavy bather loads or after weather events.

Non-chlorine Shock 

Non-chlorine shock, (potassium monopersulfate) is an oxidizer designed to enhance your pool’s existing sanitizer rather than directly kill bacteria or algae. Its main role is to break down chloramines – compounds that cause unpleasant odors and skin irritation – leaving your pool water fresh and more comfortable for swimmers.

This shock type is ideal for routine maintenance as it doesn’t alter pH, calcium hardness, or CYA levels. Unlike chlorine-based shocks, it’s safe for immediate use – swimmers can return to the pool within 15 minutes of application. 

While it’s not powerful enough for significant algae issues, it can minimize the need for harsher treatments by keeping your water consistently clean and balanced.

Assess the Severity of Your Pool Issues

Before you start throwing chemicals in the pool, it’s important to evaluate the problem at hand. If you’re dealing with a simple case of cloudy water after a pool party, a non-chlorine shock will likely be enough. On the flip side, if you’re seeing signs of algae or a drastic drop in chlorine levels, you’ll need a stronger shock treatment to tackle the issue.

• For algae growth, your best bet is cal-hypo shock. It’s fast, strong, and works at the cellular level to kill algae.
• If you’re facing consistently low chlorine levels, that indicates a bigger issue with sanitization, and you’ll want a stabilized chlorine shock, like dichlor. This will bring chlorine levels back up and prevent future drops, but keep an eye on your CYA levels to avoid overaccumulation.
• For cloudy water or bad odors caused by organic matter or chloramine buildup, non-chlorine shock is your go-to. It’s gentle on your pool’s materials, won’t raise chlorine levels, and doesn’t require long wait times before you can swim again.

Factor in Your Pool Type: Saltwater vs Traditional 

In traditional chlorine pools, you manually add chlorine, while in a saltwater pool, a salt-chlorine generator converts salt into chlorine. This means you can use the same shock treatments in both types, but with saltwater pools, a few extra considerations apply.

For instance, avoid high-chlorine shocks like cal-hypo unless you’re dealing with a severe algae outbreak, because there’s a significant risk of over-chlorination. We recommend turning off your chlorinator to prevent this. Or simply use the built-in “super chlorinate” feature of saltwater pools and shock without adding any extra chemicals. This feature can help you achieve breakpoint chlorination, effectively shocking your pool without the risk of overdoing it. 

Not to mention that cal-hypo raises calcium hardness levels, which is already a concern in saltwater pools, leading to potential scaling on your chlorinator and other surfaces over time. This could cause equipment damage, so it’s better to stick with dichlor shock or non-chlorine shock for regular maintenance.

1. 1. Safety first

2. Before you handle any pool chemicals, it’s essential to gear up for safety. Wear protective eyewear, chemical-resistant gloves, long pants, and closed-toe shoes. Pool chemicals can cause skin irritation or worse, so taking the right precautions ensures you stay safe while working with them.

1. 2. Test your water chemistry

2. To ensure you’re using the right amount of shock, start by testing your water. Use a pool water testing kit (either strips or a liquid kit) to check levels for:

• Free chlorine
• Total chlorine
• pH
• Alkalinity
• Calcium hardness

For test strips: dip them in the water and match the colors with the chart. For liquid kits, take a water sample, add reagents, and observe any color changes. Testing first helps you understand your pool’s needs and ensures you’re using the right shock dosage.

1. 3. Measure how much shock to add

2. Based on your pool’s size and the test results, calculate how much shock to add. Typically, 1 pound of cal-hypo per 10,000 gallons is recommended for standard shocking.

However, if algae is present or you’ve got serious cloudiness, you may need to double, triple, or quadruple shock your pool. Here’s what that looks like:

• Double shock: 2 lbs for 10,000 gallons
• Triple shock: 3 lbs for 10,000 gallons
• Quadruple shock: 4 lbs for 10,000 gallons

   

1. 4. Add the shock

2. If you’re using cal-hypo shock, always dissolve it in a bucket of water first. This helps prevent damage to your pool surfaces or bleaching. Pour the dissolved shock around the perimeter of the pool while your pump is running. Let the pump circulate the water for at least 8 hours (overnight is best). This ensures the shock is evenly distributed and gets to work.

1. 5. Brush your pool surfaces

2. Next, grab your pool brush and give the surfaces a good scrub. The goal here is to disturb any debris or algae, helping the shock work more effectively. By loosening debris and algae from the pool surfaces, you’re making it easier for the shock to break them down and for your filter to remove them.

1. 6. Allow the shock time to kick in

2. Now, let the pump keep running overnight. After about 8 hours, check to see if the water has improved. If your pool has gone from green or cloudy to a cloudy blue, the shock is working. If the water is still unchanged, you may need to re-shock the pool the next night.

1. 7. Clarify the Water (Optional)

2. If your water is still a little cloudy, you can use a flocculant. This chemical binds small particles together into larger clumps (or “flocs”), which are heavy enough to sink to the bottom. From there, you can vacuum them up. Just remember that this works best if your filter has a waste setting.

1. 8. Backwash Your Filter

2. After the shock has had time to work and you’ve used a flocculant (if needed), your filter will be full of dead organic debris, algae, and other contaminants. Clean the filter by backwashing (for sand or DE filters) or changing the cartridge (for cartridge filters). This step clears out all the junk your filter has trapped, keeping it working efficiently.

1. 9. Re-test water chemistry

2. After 24 hours, it’s time for another test. This ensures that the chlorine levels are safe for swimming (1-3 ppm) and that your pool’s pH and alkalinity are balanced. Adjust as necessary, and you’re all set!

• Clearer Water: After shocking, you’ll notice a significant improvement in water clarity. The cloudiness or murkiness that was present before should clear up as the shock works to eliminate contaminants.
• Restored Color: The pool water should return to its bright blue hue, a sign that impurities and organic material have been effectively broken down and removed.
• Improved Smell: A fresh, cleaner scent will replace any lingering, unpleasant odors. If the pool had a strong chloramine smell (the combined chlorine compounds), this should dissipate as the shock works to break them down.
• Enhanced Comfort: You should also notice a reduction in skin and eye irritation, which is often caused by high levels of chloramines in the pool. This indicates that the shock treatment has neutralized these irritating compounds.
• Algae-Free Water: If algae were a concern before shocking, you should see a marked improvement. Algae growth will be significantly reduced or entirely gone, and any visible green or cloudy patches in the water should be cleared. The walls and floor of the pool should also look free from any algae build-up.

Now that you’re equipped with the knowledge to choose the right shock, it’s all about understanding what works best for your pool. 

If you have a saltwater pool or a traditional one without severe algae problems, go for dichlor or non-chlorine shock. But if algae blooms are taking over, cal-hypo will do the trick. Just don’t forget to take safety precautions and always pre-dissolve the shock to protect your pool surfaces.