Why Does Pool Shock Not Dissolve? 3 Reasons

photo of undissolved shock

Pool shock is pretty magical stuff. Without it, your pool would be a clean water prison–it makes your pool water sparkle like diamonds and helps keep it clean. Pool shock can help you keep your pool water feeling inviting if you take the time and effort to use it properly.

The most common reason for pool shock not dissolving is having not been pre-dissolved before being placed into the pool. While the less common stabilized pool shocks dissolve slowly, some brands containing Calcium Hypochlorite are also difficult to dissolve. Hard water may also be the culprit. 

Pool shock lets you clean your pool’s water by killing algae, bacteria, and other contaminants. While swimming pools are an excellent feature to beat the heat in the summer, they can be a bit of a pain when you notice your shock isn’t dissolving. Let’s take a closer look. 

What You Need To Know

Using pool shock keeps your swimming pool water clear and sanitary, and several different substances are used for this purpose. It is added in small doses to water and left to circulate around the pool until it dissolves. However, this is not always the case. 

It often sits on the surface of the pool’s water or sinks to the bottom, where it can be tough to clean up. The last thing you’d want is to have wasted your time and money shocking your pool with a chemical that doesn’t dissolve. 

Related: How To Properly Store Liquid Pool Chlorine

Pool shock that doesn’t dissolve results from several factors, and it’s always bad news for your water chemistry and pool maintenance. It’s essential to understand what causes non-dissolving shock so you can create a plan for preventing this unnecessary expense.

1. Some Pool Shocks Need To Be Pre-Dissolved

Shock treatments are used to address high levels of algae in your pool. They’re similar to the chlorine we add to our pools daily, but shock treatments usually have other chemicals mixed in with them to take imminent effect.

The process is vital in maintaining water quality, whether you’ve just opened your pool for the season or are adding a new feature. But, there’s something that you need to know – some shock treatments can struggle to dissolve in your pool if they’re not pre-dissolved.

All pool shock chemicals will have an active ingredient. Those ingredients will generally either be Sodium Dichlor or Calcium Hypochlorite. When treating the water in your pool with these shocks, you should pre-dissolve the product properly before adding it to the water. 

photo of water bucket

The instructions on the back of its packaging will tell you how much of the powder you need to dissolve in a certain amount of warm water, and that measurement is based on the volume of your pool, not just the volume of water you’ll be shocking. 

If you ignore this detail, you’ll end up shocking your pool with too much or too little chemicals, which can have consequences for your health, pool, and the safety of any swimmers. 

Remember–when using pool chemicals, always use the correct measurement.

2. Stabilized Shocks Dissolve Slowly

Stabilized shocks such as Sodium Dichlor are renowned for dissolving slowly and raising the acidic levels of your pool’s water and the pH levels. 

On the other hand, it’s highly effective as a pool shock for disinfecting and oxidizing algae in swimming pools. Combined with chlorine, it creates a highly potent oxidizing agent that helps destroy organic debris, bacteria, and algae in the water.

To speed up its dissolving process, it’s recommended to pre-dissolve stabilized shocks as per their instructions on the packaging in a bucket of warm water before adding them to your pool. 

3. Your Pool pH Is Out of Balance

photo of pool test strip

When your shock doesn’t dissolve correctly, it is a perfect example of how pH affects pool chemistry. Shock temporarily raises pH, along with increasing chlorine levels. Chlorine is what kills bacteria, so pools must maintain an appropriate level of chlorine. 

When a pool has a lower pH level, the shock will be free to do its job and kill off potential contaminants. However, the shock doesn’t work as quickly and efficiently if your water’s pH is already too high. 

When your pool water has a pH of 8 or above, it’s considered hard water. The shock should be placed in water with a pH below 7.5 to be 90% effective. Therefore the shock you add to your pool will have difficulty dissolving in hard water.

When your pH is out of balance, it takes longer for your shock to dissolve, highlighting the importance of keeping pH balanced and testing it beforehand.

The next time you’re ready to add shock to your pool, you’ll want to ensure that the water is soft enough to dissolve the chemicals. 

Risks of Shock Not Dissolving

Not all shock products are the same. Shock products from different manufacturers may have different chemical compositions and require different amounts of time to dissolve and disperse in your pool.

If you add undissolved granules to your pool, they can leave stains on the pool’s floor, bleaching or discoloring it.

Calcium Hypochlorite, unlike stabilized shocks, dissolves completely when in contact with water when you follow the manufacturer’s instructions and pre-dissolve it before putting it in your pool. Therefore, no undissolved granules will be present to bleach or discolor your pool.

While Sodium Dichlor is less intense than Calcium Hypochlorite, they both stand a chance of bleaching the bottom of your pool if they aren’t dissolved correctly.

To avoid this risk, adding the shock into your pool after the sun goes down is best

Final Thoughts

Pool chemicals are designed to treat swimming pools as quickly and effectively as possible. But sometimes, they don’t dissolve as they should. There are several reasons for this. 

Using liquid shock or predisolving the shock is your best bet to avoid this issue. When doing so, following the manufacturer’s instructions and measurements is essential to add these substances to your pool carefully.

You can also avoid the risk of bleaching or scaring your pool by applying the shock in the evening instead of when the sun is shining at its brightest, which encourages this effect. 

Michael Carpenter

Hi, I'm Mike. I grew up in North Carolina having a blast on trampolines, go-karts, and just sitting on the porch with my friends. I have since moved to Las Vegas with my wife, 2 children, and 3 dogs. When I'm not chasing the kids around the house, I am probably chasing them around the backyard!

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