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Thread: Swimming after adding dichlor at shock levels -- is it bad?

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    Swimming after adding dichlor at shock levels -- is it bad?

    Here's my scenario. I have a very small above ground pool that currently has a CYA of about 20 ppm or maybe a little higher. If I had any straight cyanuric acid I would use it instead of dichlor to raise my CYA without increasing the chlorine level, but I'm using the dichlor for this purpose because it was free.

    So far I have added 4 ounces of dichlor two separate times, once about 10 days ago and once yesterday. Each time I add this much dichlor my chlorine level goes very high -- apparently higher than my OTO test can measure. Is swimming in a pool with so much chlorine bad for human health? Or is it bad for the pool vinyl?

    My son and I swam in the pool today. Although there was a very slight hint of odor from yesterday's dichlor addition we did not experience any eye or skin discomfort even though we were probably swimming at "shock" levels of chlorine. I know this is not recommended, but if we don't notice any bad effects are we doing any real damage to ourselves?
    Intex 10' vinyl above-ground pool, only 1200 gallons, with 55-gallon gravity-flow sand filter, shaded by a tree in the morning then exposed to full sun all afternoon

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    Casey's Avatar
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    Re: Swimming after adding dichlor at shock levels -- is it bad?

    We can not adequately answer your questions without a full set of test results. To do so,would be like pinning the tail on the donkey.
    I'd bet you my bikini you'll never get TFP water from a pool store!

    24' Sharkline Venture De Filter

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    Piolin's Avatar
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    Re: Swimming after adding dichlor at shock levels -- is it bad?

    8,400 gal Intex, 3K GPH pump, 16" sand filter, SWG CG-28669, TF100 test kit, speed stir, K-1766 Taylor salt test.

    The corner stone of TFP
    Pool School - Chlorine / CYA Chart

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    Richard320's Avatar
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    Re: Swimming after adding dichlor at shock levels -- is it bad?

    Effects of Adding Chemicals at the bottom of poolmath indicates that 4 oz dichlor in 1200 gallons raises FC by 14 and CYA by 13.

    So... the first time you added it, with CYA at zero, you exceeded shock level by 4 ppm FC. The excess probably burned off in the sun in a couple hours.

    The next time, CYA would have been at 13ish. No real difference in shock level but the excess probably lasted an hour longer.

    If there was any algae at all in the water -- even if you didn't see it -- the extra FC was probably gone in minutes. You may have mildly faded your liner, but probably not so you'd see with the naked eye.

    Instead of overdosing every ten days, why not use the free dichlor for your daily chlorination until you get CYA to 40 or 50? One full pound - 16 ounces - will add 50 CYA to the water. So set aside the remains of a pound of the stuff (8 ounces?) and use poolmath to calculate your daily dose until that pound is used up. We're only talking a few teaspoons a day! Yes, poolmath will tell you how much dichlor to add. It does more than just liquid bleach.

    Just be aware that dichlor is acidic, so you need to watch pH.
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
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    Re: Swimming after adding dichlor at shock levels -- is it bad?

    Effects of Adding Chemicals at the bottom of poolmath indicates that 4 oz dichlor in 1200 gallons raises FC by 14 and CYA by 13.
    Exactly! I used poolmath to figure out how much dichlor I would eventually need to add to bring my CYA up from its initial level of zero to my target of 40 ppm. The answer was 12-13 ounces. The first time I added some I had a 4 ounce measuring cup handy so that's what I used. It was teasy to use the same measure the next time too, so that's what I did.

    So... the first time you added it, with CYA at zero, you exceeded shock level by 4 ppm FC. The excess probably burned off in the sun in a couple hours. The next time, CYA would have been at 13ish. No real difference in shock level but the excess probably lasted an hour longer.
    And based on poolmath my CYA should now be 26 ppm yet my first CYA test indicated 20 ppm. This difference is probably because CYA tests are rather vague and subject to interpretation, so an error range of plus or minus 10 ppm rwould make perfect sense. Bottom line: my CYA is probably in the 20-30 ppm range now.

    Instead of overdosing every ten days, why not use the free dichlor for your daily chlorination until you get CYA to 40? Use poolmath to calculate your daily dose. We're only talking a few teaspoons a day. Just be aware that dichlor is acidic, so you need to watch pH.
    Good suggestion Richard 320, thank you. I was trying too hard to reach my final target numbers quickly so I could add the borates ASAP. From now on I'll take my time and add a little bit of dichlor every day ... and watch my pH too of course.
    Intex 10' vinyl above-ground pool, only 1200 gallons, with 55-gallon gravity-flow sand filter, shaded by a tree in the morning then exposed to full sun all afternoon

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