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Thread: Using Dichlor to Shock

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    fordfampool's Avatar
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    Using Dichlor to Shock

    This is our 2nd year with our pool. We filled the pool back up (it was drained below the returns. We tested the water after getting the pump/filter running and our tests said CYA 0, FC 0 of course, TA 90, and we have a vinyl liner so we haven't tested the CH yet.

    Last year we started out with the pool store and thus, have a ton of pucks and dichlor "pool shock" in 1lb bags. So after doing some reading on here, we saw that some people use it, so we added 2 1lb. bags per directions on the bag. (1 per 12,000 gallons).

    Next morning - FC 0 CYA 0 TA 100.

    Added 2 bags this morning and tested 2 hours later : FC 0, CYA 0, TA 100. Water looks clearish but green tinge and little cloudy.

    (I read this morning that cold water can mess up that reading so we tried again with room temp water, and it is maybe reading at 10)

    What do we do at this point? I am leary to add more of the bags of dichlor because I don't want too much more CYA and/or any other stuff that might be in those bags. But, at the same time would like to use it up if we can.

    Any advice on how we should proceed?
    thanks so much!!
    loc: WI ~24k gal vinyl w/fiberglass steps, 18ft x 38ft, 3.5ft shallow(90deg floor to walls)-8ft deep end(floor to 45deg wall to vert wall), 300lb sand filter, chlorine (liquid shock and trichlor). Skim in middle, single main, two returns facing away from skimmer and towards the surface a bit. Sarah and Mike. We are new pool owners - it came with the house!

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    JasonLion's Avatar
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    Re: Using Dichlor to Shock

    What is the PH? It is important to keep an eye on the PH when using dichlor.

    Have you read about how to shock your pool. There is a very good writeup in Pool School. Briefly, you aren't using enough chlorine.

    One handy thing to do when using dichlor is to figure out in advance how much you can use before you need to worry about the CYA level getting too high. The Effects of Adding Chemicals section of the Pool Calculator (near the bottom) is a good way to do that.
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    fordfampool's Avatar
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    Re: Using Dichlor to Shock

    Our pH is 7.6 I knew I was forgetting to list something!

    I will read that over again. I read it all but I must have missed where it says about using dichlor...I will look some more. We generally use liquid, so just a little confused on using this product.
    loc: WI ~24k gal vinyl w/fiberglass steps, 18ft x 38ft, 3.5ft shallow(90deg floor to walls)-8ft deep end(floor to 45deg wall to vert wall), 300lb sand filter, chlorine (liquid shock and trichlor). Skim in middle, single main, two returns facing away from skimmer and towards the surface a bit. Sarah and Mike. We are new pool owners - it came with the house!

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    fordfampool's Avatar
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    Re: Using Dichlor to Shock

    thanks!! I used the The Effects of Adding Chemicals section of the Pool Calculator and it says that dichlor adds 2.4 CYA for each 16oz used. Does that seem right for a pool of 24,000 gal?

    Someone posted that for every 10ppm FC you add 9ppm CYA when using dichlor. So if that is the case, and we have very little CYA in the pool now, we should be safe to add more.

    Just as soon as I think I am starting to understand pool chemistry, I realize, I have no idea

    Thanks for your help!
    loc: WI ~24k gal vinyl w/fiberglass steps, 18ft x 38ft, 3.5ft shallow(90deg floor to walls)-8ft deep end(floor to 45deg wall to vert wall), 300lb sand filter, chlorine (liquid shock and trichlor). Skim in middle, single main, two returns facing away from skimmer and towards the surface a bit. Sarah and Mike. We are new pool owners - it came with the house!

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    Smykowski's Avatar
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    Re: Using Dichlor to Shock

    To echo Jason, re-read "Shocking your Pool" and this thread.

    When you're done reading the above, read the following quote, which should help bring it all together. Then, if you still have questions, please ask. We all want to help.

    Quote Originally Posted by duraleigh
    You are not alone in that w-a-a-a-ay too many people miss the point of keeping the shock level of chlorine where it needs to be. I think a goal we can all work on here at the forum is a concise way to verbalize this process so that fewer people misunderstand.

    This isn't even remotely concise but I will try to make it clear....

    The correct way to bring your FC to shock level (for example, say 20ppm) is to calculate the dosage using the pool calculator and then add that dosage.

    Then you have to understand that that 20ppm of FC starts to reduce IMMEDIATELY upon being introduced into the pool....sometimes at very fast rates if the organic content is high and then, sometimes slower if the organics in the water are not so high. Nevertheless, in theory, you never reach 20ppm because the CONSUMABLE nature of FC means it starts to get used up instantly.

    To counteract the consumable nature of Chlorine, you must, then CONSTANTLY replenish the FC in your pool by testing, calculating and re-dosing enough FC to bring your total in the pool back up to 20ppm. This is the part that many don't recognize.....the chlorine must be CONSTANTLY replenished because it is constantly being consumed. Once you grasp the idea of testing, recalculating and redosing the question then becomes, "How often?"

    The answer is "as often as practicable". In theory, because it is continuously reduced, it has to be continuously replenished....i.e. every second of every day. Well, in reality, that is WILDLY implausible so we get back to the answer above......"as often as practicable".

    So a typical shock process goes something like this......

    Test FC = 0ppm
    Calculated dose = 20ppm

    2 hours later....
    Test FC = 12ppm
    Calculated dose = 8ppm

    6 hours later.....
    Test FC = 12ppm
    Calculated dose = 8ppm

    Next AM........
    Test FC = 4ppm
    Calculated dose = 16ppm

    Next afternoon.....
    Test FC = 6ppm
    Calculated dose = 14ppm

    6 hours later....
    Test FC = 16ppm
    Calculated dose = 4ppm

    Next AM.....
    Test FC =16ppm
    Calculated dose = 4ppm

    That evening....
    Test FC = 16.5ppm
    Calculated dose = 3.5ppm

    ...repeated continually until your water is crystal clear and you lose not more than 1ppm overnight
    (Dave wrote it in this thread. Probably needs to be a sticky somewhere. I've read just about every thread in "Swimming Pool Care" for the last 9 months, and this is by far the most misunderstood concept on this board.)
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