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Thread: Pool Shock Q

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    Pool Shock Q

    i have a Q around pool shock. my understanding of it is that shock "destroys organic contaminants and restores free available chlorine to the water", and shock is different than chlorine sanitizer. i use a little HTH pool shock in my 386gal spa on a weekly basis (maybe 1/4fl.oz) in an effort to reduce amount of Chlor Brite i use to sanitize. however, Chlor Brite says it is a sanitizer and shock, thus i am not sure i am helping any by using the additional HTH shock.

    should i find a straight powdered chlorine, or use std bleach, and HTH shock, or just stick with Chlor Brite.

    my water via current method has been clear and balanced (working on a high alk issue), and my k2006 test kit comes in a few days (test strips for now), should i change my method?

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    Re: Pool Shock Q

    "Shock" is a term used for several different products which is why we don't like to use it as a noun. Pool shock is sometimes Cal-Hypo. Sometimes shock is Dichlor, sometimes it is granular Trichlor, Sometimes it is non-chlorine shock (potassium monopersulfate aka MPS).

    Let's look at the ingredients for each of the HTH Shock products. HTH Green-to-Blue Shock Treatment is Cal-Hypo. HTH Shock 'N Swim is Cal-Hypo. HTH Super Select Shock Treatment is Cal-Hypo. HTH Ultra Complete Shock is Cal-Hypo. So the HTH products are calcium hypochlorite. That's chlorine that also increases Calcium Hardness (CH).

    Leslie's Chlor Brite is Dichlor which is chlorine that also increases Cyanuric Acid (CYA).

    The fact is that you do not need to use a shock product at all and there is nothing particularly special about the above products except that by calling them "shock" they can charge more and have you use more than you really need. You don't have to shock the pool or spa regularly either. The right way to use chlorine in a spa is to add enough chlorine after your soak to oxidize your bather waste and then add enough to maintain the FC level in between soaks.

    If you don't want to keep building up the CYA level by using the Dichlor (chlor-brite), then you can switch to using bleach, but you need to make other changes to have that work well in your spa. See the sticky at the top of the Spas & Hot Tubs section of this forum (not sure why you posted your question here since it's about what to use for spas -- maybe because you asked about pool shock?).
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    Re: Pool Shock Q

    Quote Originally Posted by Pool_Kid View Post
    .........should i find a straight powdered chlorine.........
    There is no such animal. All forms of powdered chlorine will contain some kind of binder, as chem geek pointed out it is usually calcium (calcium hypochlorite aka Cal-Hypo) or CYA (Trichlor/Dichlor).

    If your water is truly balanced, liquid chlorine (aka bleach) is all you need for daily sanitation, or to super-chlorinate (shock). Chlorine in it's liquid form (sodium hypochlorite) will contain a trace amount of salt, but there is not enough to be an issue in your pool/spa.

    Have a read through the "How to Chlorinate your Pool" article in Pool School for more info.

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    Re: Pool Shock Q

    Quote Originally Posted by chem geek View Post

    If you don't want to keep building up the CYA level by using the Dichlor (chlor-brite), then you can switch to using bleach, but you need to make other changes to have that work well in your spa. See the sticky at the top of the Spas & Hot Tubs section of this forum (not sure why you posted your question here since it's about what to use for spas -- maybe because you asked about pool shock?).
    oh, it was a Q around balancing, and the HTH stuff simply said "pool" on it. product labels do vary between "pool" and "spa", just not sure if the concentration of chemical is any diff between the two.

    @chem geek - so i read the sticky, it says to shock the water on a regular basis. below you say shock is not needed. i understand the chemistry now, but not the methods. according to the sticky i should dichlor until ca is right, then switch to bleach, and shock (using mps?) on a weekly basis?

    and do i have this right:
    ta is a buffer to ph
    ca is a buffer to fc

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    Re: Pool Shock Q

    You are right that the sticky How do I use Chlorine in my Spa says to shock once a week. We need to change that because normally this is not necessary. If one adds the right amount of chlorine after each soak and maintains chlorine in between soaks, then one normally does not need to shock (elevate chlorine levels) regularly.

    Regardless of whether one elevates the chlorine level regularly, "shock" products are not special and pool products are the same as spa products in general. We always check the ingredients to be sure and you want to get pure products if you can find them.

    Yes, you use Dichlor until the CYA is right (which you can most easily figure out by just keeping track of how much Dichlor you add) and then switch to using bleach. You shouldn't need to shock at all regularly. Try that first. If for some reason the water quality isn't good enough, then you can shock with more chlorine. I don't think MPS will be helpful for that -- chlorine usually does a better job.

    Yes, you have the buffer concept right. TA is a buffer for pH and CYA is a buffer for FC (technically for the active chlorine, hypochlorous acid). Just note that TA is ALSO a source of rising pH in its own right due to carbon dioxide outgassing. So for spas using bleach what we recommend is lowering the TA level to around 50 ppm and then using 50 ppm Borates (usually from boric acid) for additional pH buffering since the borates don't cause the pH to rise the way that carbonates do (carbonates are the normal pH buffer that is what TA is mostly measuring).
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    Re: Pool Shock Q

    spa maker recommends shocking with a MPS. comes with pros and cons

    "SHOCK TREATMENTS (POTASSIUM PEROXYMONOSULFATE)
    Even with regular sanitization, shock treatment may be necessary on occasion. Shock is recommended over super chlorination because it does not add additional sanitizer to the water. It is also effective in oxidizing wastes and will reduce chloramines or bromamines."


    There are several advantages of using potassium peroxymonosulfate in swimming pools:

    Since there is no chlorine added, the swimming pool is available for swimming immediately after the shock has dissolved and time has been given for the oxidation process to complete. Oxidation is usually complete in about one to two hours, versus eight or more hours for chlorine-based shock.
    Chlorine use can decrease, as less chlorine is needed to oxidize organic and inorganic matter in the pool.

    There are several disadvantage of using potassium peroxymonosulfate as a shock treatment in swimming pools

    Chlorine tests can read incorrectly high in DPD or FAS-DPD tests, as the non-chlorine shock may show up as combined chlorine in these tests.
    More expensive than chlorine-based shock products.
    If adequate chlorine sanitizer levels are not maintained, then adding non-chlorine shock like MSP may increase the risk of algae growth due to possible nitrate creation from adding MPS.

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    Re: Pool Shock Q

    I have been using the dichlor then bleach method to maintain my hot tub for almost two years and I have never shocked it. And I don't use MPS, only bleach after each soak and at least every other day if we don't use it which is rare. We generally use it at least 5 days a week.
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