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Thread: Free Chlorine vs. Total Chlorine adjusting

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    Default Free Chlorine vs. Total Chlorine adjusting

    What a great site, have had 18x36 vinyl in-ground pool for 15 years and
    never found such a great place for chemical answers. Using a drop based
    kit, just opened pool last Saturday. Clean and vacuum and started filter everything working well.
    Use pucks, put (4) in skimmer to start pool, but since reading here will probably change. Pool looks fair
    today a bit cloudy but moving to blue. My chlorine readings are off
    and I don't know how to get them satisfactory. Big difference from FC to TC. Here are my readings any suggestions appreciated.

    62 temp
    FC 1.
    TC 6.
    PH 7.2
    TA 100
    Hardness 100

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    Default Re: Free Chlorine vs. Total Chlorine adjusting

    Since you say your pool looks fair and only a little cloudy, I expect that maybe your results are just inaccurate. If you truly had a CC reading of 5, then I think you would be looking at a swamp. Retest your chlorine levels again. PH is OK at 7.2, but don't let it go any lower. TA and Hardness are both ok. Repost after you retest and we'll go from there. Also, run pump 24/7 while clearing the water.

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    Cool Re: Free Chlorine vs. Total Chlorine adjusting

    Quote Originally Posted by Truckman
    Using a drop based
    kit, just opened pool last Saturday. Clean and vacuum and started filter everything working well.
    Use pucks, put (4) in skimmer to start pool, but since reading here will probably change. Pool looks fair
    today a bit cloudy but moving to blue.
    My chlorine readings are off
    and I don't know how to get them satisfactory. Big difference from FC to TC. Here are my readings any suggestions appreciated.

    FC 1.
    TC 6.
    PH 7.2
    TA 100
    Hardness 100
    Quote Originally Posted by Watermom
    Since you say your pool looks fair and only a little cloudy, I expect that maybe your results are just inaccurate. If you truly had a CC reading of 5, then I think you would be looking at a swamp. Retest your chlorine levels again.
    Actually, Watermom, those readings are pretty typical for a pool freshly opened with a biofilm in place (note the cloudy water now clearing). What would be determinative, would be to find out what Truckman's CYA readings were last fall compared to now. I'll bet he has little or no CYA now, compared to moderate or high CYA when he closed. The fact that he feeds pucks (trichlor) makes this even more likely.

    What happens, is that the bacteria in the biofilm 'eat' CYA and 'poop' ammonia and urea. As soon as chlorine is added, you end up with massive CC levels. The solution is to use borax to push the pH to around 7.8, which favors the formation of monochloramine, which is the least irritating chloramine, and which also happens to be highly effective against algae and biofilms*. Then, while maintaining the pH, dose nightly with bleach, till the CC levels drop below 1.0. Continuing 'shocking' for at least a week longer, repeating doses anytime the chlorine drops below 5 ppm. This is necessary to remove any remaining urea. Unlike ammonia, it does not react instantly with chlorine.

    Obviously, on some pools, you may risk calcium carbonate cloud formation, but not on this pool. And even on those, if they have a good filter (ie, not an AG sand filter!), they'll be working on the ammonia/urea mess long enough for the calcium carbonate to filter out before it becomes a problem.

    Hope this helps,

    Ben
    "PoolDoc"

    *Interestingly, because of the monochloramine, pools which open with high ammonia AND high pH will often clear almost instantly upon addition of the chlorine. But, they may show ZERO chlorine, unless the owner tests with OTO, or runs the DPD combined test. Test strips often are 'free chlorine' only, and will show zero as well.
    Last edited by PoolDoc; 05-02-2006 at 08:37 PM.

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    Default Re: Free Chlorine vs. Total Chlorine adjusting

    OK, Ben. Now that I reread his post and your reply, I remember your explanation about cya loss/high cc upon opening. But, my pool always closes with cya (probably around 40) and I always open to none, but no cc reading - at least no more than 0.5. Why is it that the high CC shows up in some pools with cya loss over the winter and not others?

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    Default Re: Free Chlorine vs. Total Chlorine adjusting

    Total Chlorine is a 3 at this reading, however FC is still around 1. Cloudy enough that I can't see the bottom in the deep end 8'. Maybe I just need to give it more time. Pump running continious. Removed the pucks, now feeding it nothing. This may also be of some help, everytime I un-cover (looplock cover) lets trash in, the pool water is clear but the bottom and sides walls are black. I vacuum it all to waste, I repeat vacuum several times after running overnight, I then add chemicals and wait for it to clear. It sometimes takes
    weeks and sometimes only a few days. Have sand filter. Just trying to give as much info as I can. This website seems to have the knowledge that I
    need to get this thing going and keep it going in a shorter period of time.

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    Default Re: Free Chlorine vs. Total Chlorine adjusting

    Quote Originally Posted by Watermom
    OK, Ben. Now that I reread his post and your reply, I remember your explanation about cya loss/high cc upon opening. But, my pool always closes with cya (probably around 40) and I always open to none, but no cc reading - at least no more than 0.5. Why is it that the high CC shows up in some pools with cya loss over the winter and not others?
    Well, I don't know for sure. But apparently some bacterial processes can take the ammonia and further process that to nitrates. Those will fertilize future algae growth, but not have any impact initially.

    Once I've sold 100,000 kits . . . and used some of the profits to build my lab . . . I'll be able to answer some of those sorts of questions.

    Meanwhile, I can't, and nobody else seems to want to do so.

    Ben
    "PoolDoc"

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    Exclamation Re: Free Chlorine vs. Total Chlorine adjusting

    Quote Originally Posted by Truckman
    un-cover (looplock cover) lets trash in, the pool water is clear but the bottom and sides walls are black. I vacuum it all to waste, I repeat vacuum several times after running overnight
    You'll get better results if you raise the pH and dose chlorine to 15 ppm with bleach. Leave the cover partly on, to reduce solar loss.

    I wouldn't vacuum to waste, unless stuff is blowing through the filter. But, if it is, that indicates that your filter is not operating properly, and needs attention. It may be too small for your pump, or be filled with coarse sandblast sand, or simply need to have sand added. Given that it's an AG pool, you may have all three problems. AG pool filters are almost always undersized. If you have a two speed pump, the quick fix is to run on low speed, which typically moves approximately the correct amount of water for the filter, and allows the filter to actually filter the goo out, instead of the goo being forced through the sand by the excessive pressure and flow.

    Ben

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    Default Re: Free Chlorine vs. Total Chlorine adjusting

    The stuff is so thick when I open the pool, if I vacuum thru the filter the pressure will rise to 30lbs in about 10 minutes. Its like vacuuming mud and the filter can't handle such a continious flow, it eventually will start to come
    back thru the returns. I really don't believe its pump or filter problem.
    This stuff is black and taking it to waste bypasses the filter completely and
    takes it out for good. Need to add a good amount of water when this process is completed however.

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    Default Re: Free Chlorine vs. Total Chlorine adjusting

    Quote Originally Posted by PoolDoc
    Well, I don't know for sure. But apparently some bacterial processes can take the ammonia and further process that to nitrates. Those will fertilize future algae growth, but not have any impact initially.

    Once I've sold 100,000 kits . . . and used some of the profits to build my lab . . . I'll be able to answer some of those sorts of questions.

    Meanwhile, I can't, and nobody else seems to want to do so.

    Ben
    "PoolDoc"
    Ben,
    I read the links you posted in another thread about the bacterial degredation of CYA and realized that they are the same families of bacteria that are used for anerobic denitrification (a good thing!) in a salt water aquarium (and also in soil). Under dark, anerobic conditions such as a covered pool with no circualtion, it is possible that some of the urea and ammonia are broken down all the way to NO2 and N2 which can gas off out of the water, laving less urea and ammonia compouds to form CC. In aquariums the breakdown cycle (simplified) is nitrate to nitrite to ammonia (and possibly other ammonia compounds), to NO2 and N2 which leave the aquarium water. Becuase of the chemical structure of CYA (and my limited chemistry knowledge) it seems that breakdown to urea is most likely. I don't know if it is more perisitant than ammonia but I suspect it is. This probably also affects the breakdown products as well. I don't really know at this point just how urea will be degraded by the bacteria but I belive it eventually follows the same pathway.

    This is just my thoughts based on my knowlege of the process in aquariums and I intend to research it more as time permits but it is a possible explanation to watermom's question.
    11.75'x23.75' kidney 6.5K gal IG fiberglass pool/300 gal acrylic spillover spa combo; Aqualogic automation/SWCG; Pentair Clean and Clear 150 cart filter; 1.5 hp uprated 2 spd Pentair Whisperflo pump; PF:17
    Retired pool store and commercial pool maintenance guy.

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    Default Re: Free Chlorine vs. Total Chlorine adjusting HELP!

    OK, I am really losing my patience. Pool now is totally blue, looks clean but
    is still very cloudy. The surprise is I have put in over 7 gallons of bleech 6%
    in the last 36 hours, and am still only getting a 1.0 reading of FC and close to 3.0 of TC. There is no way I can get the chlorine to 15 as you suggested. PH is at 7.5 and TA is at 100. CYA is also at 100. Do I just
    wait it out? Pump is still running 24/7.

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