Swimming season is just around the corner, and no matter what kind of sanitation your home pool will be using this summer – you will need to add a shock to your pool. If you’re a pool care beginner and don’t know where to start – let alone what a shock is – we have you covered!
Here we cover everything a beginner pool owner should know about shocking a pool.
What is a pool shock?
The term shocking means to add enough chlorine to pool or spa water to destroy all combined chlorine present in the water. This usually requires adding 10 times of the amount of combined chlorine present in parts per million (ppm). The common term for using a shock to destroy combined chlorine is called “breakpoint chlorination.”
Another reason to for shocking the pool is to remove algae or bacteria, by oxidizing all contaminants in the pool. All shock treatments can be used for both purposes – for removing combined chlorine and for killing algae and bacteria.
Before we get into the different types of pool shock, here are some things to keep in mind before using pool shock:
- No matter what type of pool shock you use, it’s important that you follow the instructions on the shock label very carefully.
- Make sure that the pool shock chemicals are stored in a cool and dry place.
- Always apply pool shock chemicals directly to pool or spa water – not water to chemicals.
Which type of pool shock should I use?
The type of shock you should use will depend on the water chemistry and the reason you’re shocking.
If the water is green, you should use a cal-hypo shock. However, if you’re shocking as part of a weekly maintenance and your pool looks clean, you can use: sodium di-chlor, potassium monopersulfate or sodium hypochlorite.
Typically, it’s recommended to switch between a chlorine sock and a non-chlorine shock every other week or before or after a heavy bather load.
4 types of pool shock
Calcium Hypochlorite, or cal-hypo, is the most powerful and fast-acting shock available. This popular shock method dissolves quickly and is unstabilized. Unstabilized shocks burn off from the sun’s UV rays and do not increase cyanuric acid levels. Cal-hypo shocks will also slightly raise your pool’s pH levels.
To avoid damage to your pool surface, be sure to always pre-dissolve a cal-hypo shock before putting it in your pool. Additionally, cal-hypo shocks should be added in the evening when the sun goes down and you can enjoy your swimming pool returns to your pool’s typical chlorine levels.
2. Sodium di-chlor
Sodium Dichloro-S-Triazinetrione, also known as dichloroisocyanuric acid or di-chlor for short, is a stabilized, slow-dissolving shock method. Unlike cal-hypo, di-chlor will dissolve slowly and raise cyanuric acid levels. Typically, sodium di-chlor will increase the pool’s pH levels.
In addition to a shock treatment, di-chlor can be used as a sanitizer and oxidizer. When using di-chlor as a shock method, use 1 pound per 10,000 gallons of water. Similarly to cal-hypo, a di-chlor shock should be added after the sun goes down.
3. Potassium monopersulfate
Potassium monopersulfate is a chlorine alternative oxygen-based shock type. Potassium monopersulfate shock can be used to oxidize, destroy contaminants and help chlorine operate more efficiently. Unlike both cal-hypo and di-chlor, potassium monopersulfate won’t change your pool’s cyanuric acid levels.
4. Sodium hypochlorite (bleach or liquid shock)
Sodium hypochlorite, also known as bleach or liquid shock, is a “heavy duty” type of pool shock isn’t typically use in home pools. Sodium hypochlorite is quick-dissolving and, unlike cal-hypo, does not need to be pre-dissolved before putting it in your pool.
Sodium hypochlorite shock is often delivered by trucks and stored in 50-gallon vats and is often used in commercial pools, such as: hotels, condos and health club pools. This commercial strength liquid chlorine is also used by laundry and dry cleaners and has a strong concentration of 12.5 percent sodium hypochlorite. By contrast, most store brand bleach sold in one-gallon jugs are just 5 percent or less of sodium hypochlorite – same stuff, just contains more water. If you buy liquid bleach for your pool, be sure to get unscented and unaltered, regular bleach.
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