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Thread: Questions about some chemistry definitions

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    Questions about some chemistry definitions

    Hello all,

    I've been reading more about the different factors making up pool chemistry, and would appreciate some help with the questions below:

    - The definition of ppm is Parts-Per-Million. Millions of what? Water? Or is that just a notion of quantifying the percent of a certain chemical in the entire pool? (however being so small it's easier as ppm?)

    - Somewhere I read that it's not enough to just maintain a certain level of FC, and that it's also important to keep a 5-7% balance of FC to CYA. Why is that? What will happen if I have higher levels of CYA?

    - Continuing from the question above, should I go by target FC and then adjust CYA accordingly, or the other way around is better? (and why? )

    - So I've read that TA helps in balancing pH movement, how does it work exactly? Hypothetically, let's say I am happy being a slave to my pool and I'm happy adjusting pH three times a day (again, hypothetically!), is it important still to keep the right level of TA or does it become meaningless then?

    - If I were to add bleach to the pool as a replacement for liquid chlorine, and assuming it has a concentration of say 6%, what is the other 94%?

    - One more question I just thought of, it said somewhere in one of the other posts that during a SLAM more than normal FC is lost, why is SLAM different in that sense?

    I hope that's not too much to ask, and thanks in advance!
    Last edited by slepax; 02-03-2014 at 10:05 AM. Reason: Added one more question
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    Mod Squad JohnT's Avatar
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    Re: Questions about some chemistry definitions

    -
    The definition of ppm is Parts-Per-Million. Millions of what? Water? Or is that just a notion of quantifying the percent of a certain chemical in the entire pool? (however being so small it's easier as ppm?)
    It doesn't really matter. Could be a million grams, a million pounds or a million molecules. If you take a million anything of the mixture in your pool, if three of them are chlorine, you have 3ppm. Usually it is 1 milligram/liter in a liquid. It is just like percent, but at much lower concentrations. Rather than saying 0.0003percent (or parts per hundred), you say 3 ppm.

    Somewhere I read that it's not enough to just maintain a certain level of FC, and that it's also important to keep a 5-7% balance of FC to CYA. Why is that? What will happen if I have higher levels of CYA?
    I'm not sure what you mean by a 5-7% balance. CYA restricts the effectiveness of chlorine while protecting it from UV degradation. Too little CYA and your chlorine is gone. Too much CYA, and you require very high chlorine levels to maintain sanitation. Check out The Chlorine/CYA Chart for guidance.


    So I've read that TA helps in balancing pH movement, how does it work exactly? Hypothetically, let's say I am happy being a slave to my pool and I'm happy adjusting pH three times a day (again, hypothetically!), is it important still to keep the right level of TA or does it become meaningless then?
    TA is a measure of the buffering ability of a solution. Buffering is resistance to pH change. Google "carbonate buffering" for more information than you'll ever need.

    Depending on what your pH is, the buffering effect may be stronger at resisting rise or resisting decrease in pH. Lower TA may make your pH more unstable. High TA may make your pH want to stay at a certain point. Whether that is more than an inconvenience can depend on other things going on with your water. If you have scaling problems, the high pH can cause you big troubles. Most of the time it's just a matter of what it takes to make your pool easy to care for.

    If I were to add bleach to the pool as a replacement for liquid chlorine, and assuming it has a concentration of say 6%, what is the other 94%?
    Liquid chlorine requires high pressure, and is unsuited for pool care. What most people call liquid chlorine is just sodium hypochlorite or bleach. For pool use, it's usually 10% or 12% while for laundry use it is 6 or 8.25%. It's important to read the label because some cheap bleach is as little as 2% sodium hypochlorite. Liquid chlorine, liquid shock and bleach are all the same thing. Most of what is in a jug of bleach is water with a little lye.

    One more question I just thought of, it said somewhere in one of the other posts that during a SLAM more than normal FC is lost, why is SLAM different in that sense?
    To start with, if you are going to SLAM, you have something in the pool consuming chlorine, so that will start you on higher consumption. You are shooting for levels much higher than what your CYA can protect, so mostly it is that chlorine loss is related to the level of chlorine in the water. You lose a percentage, so the more that is in there, the faster it falls.
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    JasonLion's Avatar
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    Re: Questions about some chemistry definitions

    You should do some reading in Pool School. Most of these are answered there.

    CYA is difficult to adjust, FC is easy to adjust, so you adjust your FC level to be good for your current CYA level.

    The higher the CYA level the less active disinfecting chlorine is available (for a fixed FC level). CYA grabs onto chlorine and holds some percentage out of the action. Thus as CYA goes up you need to raise FC to maintain the same active chlorine level. The test measures all of the chlorine, active and inactive.

    The higher the TA level, the less PH moves in reaction to a give addition of chemicals. Also, the higher the TA level the more "pressure" there is on PH to go up.

    FC lost to sunlight is a percentage of the current FC level. Thus higher FC levels mean more chlorine lost to sunlight.
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