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Thread: Understanding Chlorine burn.

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    Understanding Chlorine burn.

    Hi all. Well, I just opened my pool for the season to a moderate green, I brought the FC up to 22 and ran the filter 24/7 and the next day it was nicely cleared. I tested at sunset and got 22 FC 1 CC and again at sunrise and got 22/.5 so I figured the shock process was complete and I could let my FC level drop to normal over the next couple of days. I forgot that my CYA was low at closing last season, and I had to add a fair amount of water over the winter. I tested tonight to see how things were doing and was surprised to see FC 2.5 CC 0. I'll run a full battery of tests tomorrow but obviously my CYA is very low.

    My question is, how much chlorine will burn of by the sun with little to no CYA? Hypothetically, if my FC level was 50 could it burn off in one day of strong sun? Or is there a maximum that would burn off during the day?

    On a side note my bleach supplier (walmart) has repackaged their bleach to an 8.25% concentration 121 oz bottle. The pool calculator doesn't list that size for the calculation of how much to add/what level increase you get. Is the formula available or has anyone done a conversion.

    Thanks,
    25000 gal IG gunite plaster. Built in spa, built 1984.
    48 SF Hayward DE-4800 filter
    1 hp Hayward super pump
    3/4 hp Polaris PB-4 booster pump, Polaris 380
    Taylor K-2006 test kit

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    pwrstrk's Avatar
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    Re: Understanding Chlorine burn.

    If you use the closest jug size you'll be ok. The sun will burn a lot of chlorine off with low or no CYA.


    Jeff
    24'x54" AG Morada RTR (by wilbar) 13'500 gal. Hayward Powerflo Matrix 1hp 2 speed. Hayward Perflex EC65 DE filter.

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    Mod Squad jblizzle's Avatar
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    Re: Understanding Chlorine burn.

    Why did you raise the FC so high if you had not tested your CYA level? That did not really follow the methods of accurate testing and dosing.

    You will lose a % to the sun, at no/low CYA, that will be a very high percentage.
    Jason, TFP Moderator
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    Richard320's Avatar
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    Re: Understanding Chlorine burn.

    Quote Originally Posted by dickeystorm
    Hi all. Well, I just opened my pool for the season to a moderate green, I brought the FC up to 22 and ran the filter 24/7 and the next day it was nicely cleared. I tested at sunset and got 22 FC 1 CC and again at sunrise and got 22/.5 so I figured the shock process was complete and I could let my FC level drop to normal over the next couple of days. I forgot that my CYA was low at closing last season, and I had to add a fair amount of water over the winter. I tested tonight to see how things were doing and was surprised to see FC 2.5 CC 0. I'll run a full battery of tests tomorrow but obviously my CYA is very low.

    My question is, how much chlorine will burn of by the sun with little to no CYA? Hypothetically, if my FC level was 50 could it burn off in one day of strong sun? Or is there a maximum that would burn off during the day?

    On a side note my bleach supplier (walmart) has repackaged their bleach to an 8.25% concentration 121 oz bottle. The pool calculator doesn't list that size for the calculation of how much to add/what level increase you get. Is the formula available or has anyone done a conversion.

    Thanks,
    I'm not sure how fast it will burn off. I'm sure chemgeek has posted something. I do know you lose percentages, not fixed ppm, so the higher the FC, the more ppm you lose. Try the search box using terms like degradation or breakdown.

    As for the new 8.25%, the only difference is that the number of jugs is wrong - it still will calculate ounces just fine if you enter the strength.

    You should always start with a full set of results! Especially when performing the shock process or asking advice about your pool chemistry. What if CYA is 150? Then your massive loss would be worrisome! If it's 10, you overdid the bleach and probably wasted a lot of it due to the aforementioned UV breakdown.
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
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    Re: Understanding Chlorine burn.

    Thanks for the replies. As to why I went to 22 FC, umm, mostly laziness , I saw green and wanted to knock it down fast since I had a mountain of other work to do and I just didn't take a moment to think.
    25000 gal IG gunite plaster. Built in spa, built 1984.
    48 SF Hayward DE-4800 filter
    1 hp Hayward super pump
    3/4 hp Polaris PB-4 booster pump, Polaris 380
    Taylor K-2006 test kit

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    Re: Understanding Chlorine burn.

    If there was no CYA at all, then you would lose around half of the FC per hour at peak noontime sun. Going from 22 to 2.5 would be a 50% per hour loss rate over a little more than 3 hours so it's definitely plausible (22 to 11 to 5.5 to 2.75 to 1.38, etc.). You might have a tiny amount of CYA in the water or their might not have been full sun on the pool.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

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    Re: Understanding Chlorine burn.

    Thanks chemgeek. I ran a full battery of tests today. There was no cya much to my surprise.
    FC 7
    CC .5
    CH 290
    TA 160
    CYA appeared to be nonexistent, filled tube with no sign of cloudiness

    So, I've started to add CYA. I put enough into the skimmer to get to 20 with the final goal of 40. I may go higher to combat the strong southeast TX sun. I've added a bunch of trichlor tabs in floaters for now to try and keep the FC up and to help raise the CYA.

    Thanks again for the input
    25000 gal IG gunite plaster. Built in spa, built 1984.
    48 SF Hayward DE-4800 filter
    1 hp Hayward super pump
    3/4 hp Polaris PB-4 booster pump, Polaris 380
    Taylor K-2006 test kit

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