When someone says they need to “shock” their pool to kill algae, eliminate scum or get the water chemistry back to the levels it needs to be fast, everyone knows it is a chemical treatment of some sort. However, fewer people are familiar with the different types of pool shock, much less the pros and cons of each type of pool shock.
All pool shocks are an oxidizing compound or mixture of oxidizing compounds that destroy chloramines and other substances you don’t want in the pool.
Calcium Hypochlorite Shock
It consists of 65% available chlorine plus other compounds.
Pros of Calcium Hypochlorite Shock
Calcium hypochlorite is the most popular pool shock because it is the cheapest type of pool shock.
Super-shocks with 73% calcium hypochlorite are available to kill algae and substances with a bio-film.
The chlorine in this type of pool shock kills bacteria quickly.
Cons of Calcium Hypochlorite Shock
Pre-dissolve is required to use this properly.
If you have well water that has high levels of pre-existing minerals, the pool shock won’t work as well.
This type of pool shock is corrosive and can damage any type of pool liner. Don’t pour it on top of the pool skimmer or you’ll risk oxidizing (rusting) it faster. Don’t pour it directly into the side of the pool in concentrated form or you risk bleaching the pool liner.
It can leave behind shock dust residue after use.
It can be hard to find in some parts of the country.
Using too much leaves the pool with a high pH.
This is hazardous to store safely and transport.
Tips for Using It
Calcium hypochlorite pool shock is best added at night. This maximizes the effectiveness of the chemical reaction, as well as minimizes the hassle of the eight hour wait time you need after adding it.
Always add pool shock to water instead of water to shock. With this type of pool shock especially, be careful not to get it on your skin or you risk chemical burns.
Lithium Hypochlorite Shock
Lithium hypochlorite pool shock is around 35% available chlorine.
Pros of Lithium Hypochlorite Shock
This type of pool shock works when your water has high levels of calcium (hard water) naturally.
It doesn’t require pre-dissolve to work.
This type of pool shock is less likely to bleach or stain the pool liner.
It doesn’t cloud the water like calcium based pool shocks.
You can use lithium hypochlorite pool shock in fiberglass and vinyl lined pools.
Cons of Lithium Hypochlorite Shock
This type of pool shock costs more than calcium hypochlorite.
You can’t get as high a percentage of available chlorine with this type of pool shock, which requires using more of this expensive type of shock when you need more chlorine in the water to get the chemistry right.
Tips for Using It
This type of pool shock like the prior one is best added at night and has an eight hour wait time.
DiChlor Shock
DiChlor is the common name for Sodium Dichloro-S-Triazinetrione, a type of granular chlorine. This compound is sixty percent chlorine.
Pros of DiChlor Shock
You don’t have to pre-dissolve it before adding it.
It dissolves quickly.
This type of pool shock is pH neutral.
DiChlor contains a chlorine stabilizer in the form of cyanuric acid. You don’t need to add as much chlorine to the water if you use this substance, because the chlorine stabilizer helps prevent it from breaking down on exposure to sunlight.
It doesn’t add calcium to the water, which is a major draw if you have hard water already.
Some brands of this product have borates in them as well as the main chemical; borates help remove dissolved carbon dioxide from the water to help prevent algae from growing.
Cons of DiChlor Shock
It is expensive.
It is almost impossible to find in one pound bags if you don’t want to buy a lot at once.
Tips for Using It
This type of pool shock is popular for spring openings of a pool as you try to get the chemistry started. This type of pool shock requires you to wait eight hours before using the pool.
Potassium Peroxymonosulfate
Potassium Peroxymonosulfate, also called MPS and potassium monopersulfate, is an oxidizing agent used as a pool shock.
Pros of Potassium Peroxymonosulfate
The biggest draw of Potassium Peroxymonosulfate is that it is a non-chlorine pool shock. This is important in households dealing with chemical sensitivity.
It doesn’t require pre-dissolving.
You can add it any time. Adding it while it is exposed to sunlight won’t diminish its effectiveness.
You only have to stay out of the water for fifteen minutes.
Cons of Potassium Peroxymonosulfate
Most of these products cannot be used in a pool with a Biguanide system like Baquacil.
It causes chlorine tests to incorrectly read high on the DPD and FAS-DPD tests.
Tips for Using It
This type of pool shock can be used in bromine pools. Be careful using this pool shock after using chlorine based shock, or the combination actually increases the risk of algae growth.
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