As a pool owner, you’re gonna need to learn how to shock a pool.
Pool shocking doesn’t mean sending 5000 volts of electricity through the water (although that would be pretty cool to see).
However, what it does refer to is the rebalancing of pool chlorine levels, keeping the pool water safe to swim in.
How To Shock A Pool
Learning how to shock a pool doesn’t have to be a convoluted process. Follow these steps and you’ll become a pool shocking master in no time.
Step 1. Test & Balance Your Water
Before you add shock treatment, you need to test your pool water and balance its levels. The pH level should be between 7.2 and 7.6, with total alkalinity being between 80 and 120 ppm.
Pool water testing is easy to do using test strips or liquid test kits. They give you quick and accurate readings regarding the chemical levels in the pool. Balancing the water can be done by adding more chemicals to raise or lower the pH level until it is neutral.
Step 2. Suit Up
Anytime you’re using pool chemicals, you want to practice good safety protocols.
Wearing the appropriate protective attire is a must. When working with pool shock, you should wear gloves, eyewear, and clothing you don’t mind ruining. This is because chlorine can bleach, and accidents do happen. Chlorine fumes can also irritate your nasal passage and lungs if breathed in.
So be mindful of the power of pool chemicals. I’m sure you’d rather not have to deal with damage to your pool’s deck, finish, or yourself for that matter!
Step 3. Do Some Math
Next up is determining the amount of shock needed for your pool. As a general rule, 1 lb. of shock is used for every 10,000 gallons of pool water.
Most shock is sold in 1 lb. bags, making it easy to calculate how many bags your pool will require. Note: we recommend reading the instructions as some pool shock can vary in its dosage.
To calculate your pool size in gallons, the formula used is Length (ft) x Width (ft) x Depth (ft) x 7.5. The majority of backyard pools are usually built at 10,000 or 20,000 gallon sizes.
You should also be aware of the pool’s combined chlorine level, so that when you shock its reaching breakpoint chlorination. 10 times the amount of the combined chlorine level must be added to the pool water in order to raise its free chlorine level and reach breakpoint.
To find out your combined chlorine level, test your water and subtract your free chlorine level from the total chlorine level.
Step 4. Make A Shocking Solution
If using granular shock, you’ll need a 5 gallon bucket for this part.
Start by filling the bucket with water (about ¾ full), and then adding in 1 bag of shock. Always add the shock to the water – not the other way around.
Using a wooden stir stick, mix the solution until the shock is fully dissolved. This will help disperse it evenly in the pool and save your liner or pool finish from being damaged.
If you are using liquid shock, you can add this directly to the pool water (be very careful!)
Step 5. Add Shock To The Pool
If using dissolved granular shock, make your way around the perimeter of the pool and slowly pour the solution into the water. What this allows for is the power of the return jets to circulate it quickly. If using liquid chlorine, pour it around the perimeter of the deep end of the pool, and close to the surface to avoid it splashing up.
In some cases with granular shock, you may end up with undissolved granules on the walls of the pool, or at the waterline. Take out a pool brush and remove them pronto. These little granular buggers can damage the liner/finish if left to their own devices.
Also, make sure your pump and filter are running all night. This ensures the pool shock will be fully distributed in the water to destroy all contaminants.
Step 6. Repeat (If Necessary)
As discussed earlier, the bigger the pool, the more bags of shock that will be required to superchlorinate the water. If this sounds like your pool (anything 30,000 gallons and up), repeat this process as necessary.
Additionally, if your pool is extremely green with algae, shocking the pool more than once may be required. If this is the case, you should wait 24 hours between shocks. This is mainly due to the fact that it should only be done once the sun has gone down, so you have a limited window of when the shock will be most effective.
Need A Refresher?
Remembering how all the different chemicals interact to keep your pool clean can be confusing at the best of times, and daunting at the worst of times.
Here’s a quick crash course when it comes to pool shock.
What Is Pool Shock?
Pool shock is a “super dose” of granular pool chlorine that oxidizes chloramines (combined chlorine) and kills bacteria in the water.
Shocking depletes combined chlorine and increases free chlorine.
If your chlorine levels are low, a chlorinated shock is required. If levels are already high, you should use non-chlorinated shock.
Pool shocking is usually done at night, when the sun no longer shines on the water. This is because UV rays destroy chlorine at near warp speed. Twilight hours give the shock an extended amount of time to effectively kill everything in its path.
Why Shock Your Pool?
Over time, as chlorine works to destroy contaminants, the combined chlorine level rises and this is far weaker as a pool water disinfectant.
By shocking your pool, you replenish your chlorine level and oxidize chloramines (combined chlorine), which are a gaseous irritant that are hazardous for human consumption.
Your swimming pool may need to be shocked if any of the following scenarios have occurred:
- There’s an increase in pollutants: Pools are subjected to many changes in water chemistry. This contamination can be from rainfall, outside temperature shifts, backyard debris, and organic matter left behind after heavy pool use.
- Algae growth in the pool: Algae blooms are usually controlled by applying an algaecide to the pool. But when you need to eradicate it, a shock—or triple shock—will do just that, clearing up the water at the same time.
- There’s a buildup of chloramine: Chloramines are what we all know as that pungent dose of “pool smell”. They’re a gas that forms as a result of used up chlorine, and an indication there’s not enough chlorine in the water. Chloramines irritate your eyes, nasal passage, lungs, and skin. If the pool has a very strong chlorine smell to it, you know it’s time to shock.
- Clearing up cloudy water: Pools can get cloudy from insufficient chlorine, or an abundance of chlorine. The sweet spot for chlorine levels is between 1 and 3 ppm. Cloudy water is usually the result of an imbalance in pool water chemistry, and shocking the pool is an easy way to restore clarity to your pool’s water.
How Often Should You Shock Your Pool?
The frequency of pool shocking isn’t set in stone, and it really only needs to be done when your water starts going haywire.
Some things you’ll be able to visually see (ie. cloudy water, algae turning it green), but most water pollutants will be invisible.
There are some pool owners who like to shock once a week to keep the water its cleanest, while others will do it on a 3-week or monthly cycle.
Shocking frequency also depends on how much use the pool is getting, and what kind of weather it’s being subjected to. Heavy rainfall and storms can disrupt the pool water’s chemical makeup by introducing backyard debris and air pollutants like dust and pollen spores into the water.
Likewise, an increase in the number of people using the pool will bring in more organic bacteria, resulting in a chlorine level decrease. If you have a pool party, you’ll most likely have to shock the pool once it’s over.
You’ll also want to apply shock treatment when opening the pool, and closing it down for the season.
On opening, after you’ve balanced it’s pH level, shocking will sanitize and oxidize the pool, restoring its clear water. On closing, pool shock is used as a disinfectant to prepare the pool for the winter months.
Also of note, if you were wondering, you can’t overshock a pool. The worst that will happen is the water has an abundance of chlorine for a few hours. Once the sun comes out, it will quickly destroy the chlorine and bring the pool back to a level that is safe for swimmers.
How Long Should It Take to Shock Your Pool?
Shocking the pool only takes a few minutes of your time, but the waiting out process should be a few hours at the least.
As shocking is best done at night, it gives the pool a solid 8 hours to circulate the chlorine and fully disinfect the pool.
However, in situations which call for non-chlorinated shock, you can be back in your pool 15 minutes after its application.
What Are The Different Types of Pool Shock?
With different pool shocks or shock products are available, how do you know which one is best for your pool?
Here’s a breakdown of the top 3 pool shocks.
- Calcium Hypochlorite: Commonly referred to as cal-hypo, this shock is the most popular option, and contains 70% (or more) chlorine for killing algae and contaminants. It’s unstabilized nature means the sun will burn it off and it won’t increase cyanuric acid (CYA) levels in your pool.
Cal-hypo has a high pH and will temporarily raise those levels, so it’s a good choice for pools that test at a normal or low pH level. Of note, your water may become temporarily cloudy, and cal-hypo may also increase your water’s calcium hardness.
- Dichlor: Sodium dichlor is 55% chlorine and stabilized, which means it contains CYA. This makes it last longer in your pool water than cal-hypo, and the lower pH level and lack of calcium will keep the pool from getting cloudy.
However, because it contains CYA, CYA levels can increase. This has to be carefully monitored otherwise you may need to invest in a CYA reducer, or even drain/dilute your pool.
- Non-Chlorine Shock: Also known as Potassium Monopersulfate (MPS), this is a chlorine-free shock that oxidizes contaminants, but won’t rid the pool of bacteria. Compared to chlorinated shock, you can use MPS shock at any time of day and be swimming in the pool 15 minutes later. It’s pH neutral so your level won’t fluctuate, and by focusing on oxidation, it frees up the pool’s chlorine to be more efficient at sanitizing.
It’s Shockingly Easy
Learning how to shock a pool isn’t rocket science, and it’s something everyone pool owner should learn to do.
By understanding how different types of chlorine shock affect the pool’s water, how to use them, and the best time(s) to shock, you’ll keep your pool clean and clear with little to no trouble at all.