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Thread: Does CH affect CSI? Please help!

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    Does CH affect CSI? Please help!

    I just did my water testing and here are my results where CSI = -.23
    CH 3.5
    FC 0.0
    PH 7.8
    TA 7
    CYA 40
    CH 450
    Borates 50
    Temp is 35F

    I noticed when I used the pool calculator, if I adjusted the ph to 7.6, it would change the CSI to -.39! I always thought I need to keep my PH around 7.6 to 7.4? However, the CSI shows it to be more dangerous. I was thinking to partially refill to bring the CH down to 300 but it also showed a drastic change to CSI to -.53. How does CH affect this? Please advise.

    Also, to partially refill, can i just put the hose at the bottom of the pool and let it run?
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    mas985's Avatar
    Join Date
    May 2007
    Pleasanton, CA

    Re: Does CH affect CSI? Please help!

    PH affects CSI most, TA and CH less so on a percentage basis. However, the general consensus is that a CSI between -0.5 and +0.5 is fairly harmless and some have experienced no ill effects at even higher extremes. Also, a CH of 450 is on the high end but I have managed my pool at much higher CH so there is no urgent need to replace water but the higher the CH the harder it will become to maintain CSI in a reasonable range.
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    JasonLion's Avatar
    Join Date
    May 2007
    Silver Spring, MD

    Re: Does CH affect CSI? Please help!

    When the water is very cold you should allow the PH to rise a little, which it will tend to do naturally. This keeps the CSI in balance. Lower temperatures lower CSI, while higher PH raises it back up. As it happens, the PH will change of it's own accord as the temperature changes, assuming there is nothing driving the PH in any particular direction. Thus, the CSI tends to remain more or less constant in a closed pool as the temperature changes (though various things can disturb this balance).

    CSI changing from -.23 to -.53 isn't what I would call a drastic change. It isn't worth micro-managing CSI. It will tend to wander around some and you should allow that as long as it isn't heading too far out of range.

    CSI stands for the calcium saturation index, how saturated with calcium the water is. Therefore, the CH level has a significant impact on the CSI level. As it happens, the effect of PH is larger than the effect of CH, but still it is mostly about the CH level.

    I hope your TA level is actually 70 (as your CSI levels imply). If TA is 7, it is way too low and should be raised.

    Sure, putting the hose in the pool and allowing the pool to fill is fine. Just remember to turn the water off and take the hose out before it gets too high.
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    Re: Does CH affect CSI? Please help!

    We have learned that the harder water sinks to the bottom of the pool, so if you must drain ( ) you should put the hose as low in the pool as you can. Do not run the pump either while you are draining, as that will "blend" the water and slow your progress/results.

    Watch your plaster exposure (if you have plaster) if you do this when the weather is warmer (not sure when you plan to do this). Plaster odes not like to be exposed and does not like heat either!

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