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Shocking Your Swimming Pool- What is it and What does it do

15,Jul 2022
While caring for your pool, you may be wondering why you need to shock, when you need to shock, and how much shock you need. In this article, our pool care experts put together a guide on shocking your pool to help answer these questions and teach you everything you need to know about shock.

What is Shocking?

Shocking the pool is the process of adding a highly concentrated dose of chlorine to your pool water to prevent or resolve specific problems. Shock can help prevent the growth of bacteria, algae, and chloramines. This works by raising the level of free chlorine in the water. Also, shock can help remove these substances if they find their way into your pool.

Why Do I Need to Shock My Pool?

Three main issues can be solved by shocking your pool, including the removal of:
  • Algae
  • Bacteria
  • Chloramines
Shock will help you prevent and remove:
Algae
Algae is an organism that can destroy your pool when left to multiply. If it takes root and spreads, it can be removed with algae. You can use shock in addition to algaecide to destroy algae by breaking through their outer shells and disrupting their cellular processes.
For light green or isolated algae, you will need around ten ppm of added chlorine to kill it off. If you have medium green or yellow blooms, it may require 20 ppm. For a pool with dark green or black algae, you will likely need to add enough shock to reach 30 ppm to eradicate the algae.
Before and after shocking, our pool care experts recommend that you vacuum and brush the pool. You then want to filter the pool nonstop and backwash it as needed. After this process, you can also use a pool clarifier to clear up the pool water.
Bacteria
Viruses, parasites, and bacteria can live in your pool water, cause various issues, and be a health hazard. In a public pool, E. coli, cryptosporidium, and giardia are common, but routine sanitation measures and filtration will prevent and remove most bacteria. If you want to be sure that your pool is sanitary, you can shock your pool.
We recommend shocking your pool after heavy use; if the water has sat stagnant or has gone for a while with little to no chlorine, you will need to shock your water. When shocking to kill bacteria, the amount of bacteria present in the water will dictate how much shock you use.
You will need to test for bacteria using a bacteria test kit. Then we recommend your add enough shock to bring the pool water to 30 ppm. the amount of shock you need to kill the bacteria will depend on the amount of bacteria and the extent of the pool’s contamination. For example, E. coli is relatively easy to kill, only requiring 2-3 ppm of chlorine.
Chloramines
If your pool smells strongly of chlorine, it means that your chloramine bonds are at a high level. While it may seem ineffective, your pool needs to be shocked.
We recommend using a DPD test kit to measure the FAC and the Total Available Chlorine (TAC) levels. To balance your water, you need to shock the pool to a level that is 100 times greater than your current chloramine level. For example, if you have a chloramine level of .4 ppm, you will need to add enough shock to reach 40 ppm.

How Do I Determine How Much Shock I Need?

When you shock the pool, you need to reach a level of breakpoint chlorination where the molecular bonds break apart. There is also the point where the bacteria, algae, and chloramines are removed from the water.
In most cases, you need to get your pool up to 30 ppm of chlorine which will put you at the breakpoint of chlorination. Based on 10,000 of water, there is a reference guide for the type of shock and how much you will likely need to increase the levels by ten ppm:
  • Calcium Hypochlorite- 1.3 lbs
  • Sodium Hypochlorite- 3.5 qts
  • Lithium Hypochlorite- 2.5 lbs
  • Dichlor- 1.5 lbs
Before you add shock to the pool, check for proper water balance. If you have a high pH between 7.8-.8.2, it can leave half of your pool shock inactive.

How do I Shock My Pool?

We’ve put together a list of steps you need to take to ensure you get the most out of your shock:
Clean the Pool
Remove leaves, debris, and other materials from your pool’s floor and walls. You don’t want to waste your chlorine’s killing power on removing dirt and debris.
Adjust the pH
You need to lower your pH before shocking the pool if your pH is high. This is because chlorine works slowly when pH levels are high. Additionally, if your pH is at 8.0, less than half of the chlorine will be effective because it won’t turn into hypochlorous acid, which kills things like algae and bacteria. Be sure to lower the pH to 7.2 before you shock the pool.
Check Your Labels
There are a variety of pool shocks out on the market, each with different dosages. Check the labels, as some pool shocks require a dilution bucket to dissolve the granules and prevent pool damage.
Add in the Shock
Distribute the chlorine throughout the pool’s surface while the pool pump runs. Take care to avoid spilling any shock on your clothing or the pool deck. We recommend that you add the shock slowly and closely to the water’s surface. You also need to avoid shocking the pool on windy days, as this can blow the shock away from the pool as it is being distributed.
Brush Down the Pool Surfaces
By brushing down the pool surfaces, you can help evenly distribute the shock while removing the layer of dust or film accumulated on the pool surfaces. You will want to perform a good brushing, vacuuming, and backwashing of the pool after shocking.

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