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    The Many Types of Pool Shock

    April 7, 2014


    New pool owners get a chuckle out of the term pool shock - I think they imagine an electrical shock. Once I was asked what equipment is used to deliver "the shock" to the pool.

    It's called Shocking the Pool, because the level of chlorine (or non-chlorine oxidizer) is raised to high enough level where everything is oxidized, or blown apart, on a microscopic level. Like an electric shock, I guess.

    When to Shock the Pool

    Some pool stores may tell you to shock the pool weekly, but that's really too much. When you open the pool for spring, you may need to shock heavily, or more than once. During the early and late swim season, I probably shock the pool on a monthly basis. When the weather gets hot, and the pool is used more, I increase it and shock the pool every 2-3 weeks.

    algae-attack-packThe reason to shock the pool is to remove any bacteria in the water, or to help clear cloudy water, and to remove combined chlorine, or chloramines. If you see algae growing during the season, that's another good time to shock the pool. Depending on how bad the algae is - you may need a double or triple dose of shock, or try our Algae Attack Packs, designed specifically for Yellow, Green or Black algae.

    Types of Pool Shock

    SPP has a wide variety of pool shock treatments for swimming pools. Below is a list of four pool shock types, along with some pros and cons of each.

    1. Calcium Hypochlorite:

    The most common type of pool shock, available in 1-lb bags, or in 25 or 50 lb buckets. In the 1-lb bag version, we have 5 different formulations of Cal Hypo. They all have different strengths, or % of Available Chlorine - and some have additional chemicals added to buffer and clarify the water.

    Pros: Cal Hypo is the cheapest pool shock you can buy, and most easily available. It's also the strongest pool shock in terms of oxidation power.

    Cons: Cal Hypo is corrosive, and should be pre-dissolved before adding. 65% cal hypo has 35% calcium, adding to calcium hardness levels.

    SPP Pool Shock

    spp-pool-shockCalcium Hypochlorite - in our 1 lb packs we have a 68% Available Chlorine strength and 73% Super Pool Shock, the strongest available. In our 25 and 50 lb buckets, we have a 68% available strength of Cal Hypo.

    HTH Pool Shock

    hth-pool-shockHTH is a brand name that been around for years. They have a patented process that makes super fine granules that dissolve quickly, and it's pH buffered. We have the 45% Available HTH shock 'n swim, or their 53% strength HTH Super shock 'n swim. Both are sold in 1 lb bags.  

    Instant-Liquid Pool Shock

    instant-liquid-chlorineInstant Liquid Pool Shock is a granular chlorine in a quick dissolving formula that pours easily from the fluted bottle design. Instant Liquid dissolves instantly, no pre-mixing required, and is the strongest 73% available chlorine. Nothing is more powerful! Sold in 1 lb bottles.

    2. Lithium Hypochlorite:

    Sold in 1 lb bags, Lithium Hypochlorite is an very fine powder that dissolves instantly; safe for all pool types.

    Pros: No pre-dissolve needed, swim immediately. Leaves no residue or "shock dust", calcium-free pool shock.

    Cons: More expensive pool shock, low available chlorine strength.

    SPP Lithium Pool Shock

    lithium-pool-shockClean burning, fast acting pool shock leaves your pool water crystal clear, will not cloud water like calcium based shocks, and leaves no residue behind. Safe for all pool types without pre-dissolving. Lithium pool shock is 35% available chlorine. Not powerful, but clean acting and pH neutral.  

    3. Sodium Dichloro-S-Triazinetrione:

    Di-Chlor, as we call it around here, is the only stabilized form of chlorine pool shock. It's used as a regular chlorine method, or as a periodic shock treatment. Di-Chlor shock has some cyanuric acid mixed into the powder, to protect the shock from the sun.

    Pros: Stabilized, pH balanced, long lasting in the water, can be used during the day. Doesn't add calcium.

    Cons: More costly than cal hypo, but less than other non-calcium pool shocks. Not sold in 1 lb bags.

    SPP Dichlor Pool Shock

    Dichlor-shockDichlor is a fast dissolving, clean burning and pH neutral pool shock. SPP granular Di-Chlor pool shock is sold in several size pails or buckets, up to 50 lb size. Di-Chlor shock has 56% available chlorine strength.  

    Assure Multi-Shock


    Put the power of Borates to work in your pool! Assure Multi-Shock is a 58% Sodium DiChlor pool shock, that contains the Assure Conditioner, which removes carbon dioxide from the pool water (a favorite food of algae). Sold in 1 lb bags.  

    4. Potassium Monopersulfate:

    I call it non-chlorine pool shock, but your can also call it Potassium Peroxymonosulfate. Fast acting oxidizer does the same thing as chlorine shock, destroying everything in the water! Used on chlorine free pools, or as a safe shock to use on vinyl liners.

    Pros: Fast acting, non-chlorine formula is safe for all pool types. Swim immediately, and calcium-free.

    Cons: More expensive than chlorine pool shocks.

    SPP Chlorine Free Pool Shock

    chlorine-free-shockChlorine Free pool shock uses the power of oxygen. Unaffected by the sun, no per-dissolving required and you can swim immediately. Solid in 1 lb bags. 43% Potassium Monopersulfate (MPS), with a minimum of 4.5% available active oxygen.  

    What Type of Shock is Best for Your Pool?

    Chlorine complaintThe type of shock you use for your pool may depend on what type of pool surface you have. Vinyl pools should be shocked more gently than plaster pools, with a lower percentage of available chlorine and a quick dissolving and gentler formula, such as offered with Lithium and Chlorine Free pool shocks. If you use Cal-Hypo in a vinyl pool, be careful to pre-dissolve completely, and don't overdose.

    If you are located in a hard water area, and you have problems with high calcium hardness levels, you may want to avoid calcium hypochlorite, which will add small amounts of calcium to the pool each time you shock.

    Dichlor shock is favored for spring openings, as it will keep a high reading for days. It's also useful for chlorinating small outdoor pools, ponds or fountains, with a small scoop once or twice per week.  

    Debbie Farnan
    SPP Pool Expert  

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