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Thread: Why Difference in Pool School Recommended CH Levels - Bleach vs SWG for Plaster Pool?

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    Why Difference in Pool School Recommended CH Levels - Bleach vs SWG for Plaster Pool?

    I was just wondering why the Pool School Recommendation for CH is so much different for Bleach vs. SWG for plaster pools? It's basically the same for other pool types, but pretty different for plaster pools (250-350 for bleach vs. 350-450 for swg). My pool is in enclosure and adjust the target CYA due to it being not directly in sunlight due to UV filtering of screening, I didn't know if screening would make a difference with target levels for CH. Just trying to understand why so I can do a good job of maintaining my pool.
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    Mod Squad JVTrain's Avatar
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    Re: Why Difference in Pool School Recommended CH Levels - Bleach vs SWG for Plaster P

    The answer is in CYA level. For bleach pools, CYA is recommended 30 - 50 ppm. For SWG, 70 - 80 ppm. All other levels being equivalent, plug 50 ppm CYA in on one side of Pool Math and 80 ppm on the other (Now and Target columns). Now look at the resulting CSI difference. Higher CYA levels make the water more corrosive (more CSI negative). Increasing CH by about 100 ppm is the easiest, most permanent way to offset this CYA difference.
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    Re: Why Difference in Pool School Recommended CH Levels - Bleach vs SWG for Plaster P

    OK thanks - my CSI has been in the -0.50 to +0.10 range with my CH sitting right at 250 for past month. My CSI from last test was -0.07 which I understand to be a good target.
    FC: 2.8
    CC: 0
    PH: 7.8
    TA: 80
    CH: 250
    CYA: 50
    Temp: 84
    Salt: 3400

    Plugging 300 into the Pool Math makes my CSI a perfect 0, but I had thought I read that slightly negative was better. Based on this any reason to move the CH to 300 or 350?
    Free Form 13K IG (Quartz) w/Screen Enclosure - 2 Sheer Descents, 1 Bubbler - Hayward 60 SF DE Sta-Rite - Hayward SP3400VSP EcoStar - Hayward Aqua Rite AQR9 (T-Cell-9) SWG - Zodiac MX6 - July 2016 - Taylor K-2006 - Taylor K-1766 Salt Test

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    Mod Squad pooldv's Avatar
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    Re: Why Difference in Pool School Recommended CH Levels - Bleach vs SWG for Plaster P

    Slightly negative is better for your salt cell and if your water has a tendency to scale, pH rise and/or higher TA. -0.3 to 0 is ideal. But, -0.3 to +0.3 is good.
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    Re: Why Difference in Pool School Recommended CH Levels - Bleach vs SWG for Plaster P

    Thanks!
    Free Form 13K IG (Quartz) w/Screen Enclosure - 2 Sheer Descents, 1 Bubbler - Hayward 60 SF DE Sta-Rite - Hayward SP3400VSP EcoStar - Hayward Aqua Rite AQR9 (T-Cell-9) SWG - Zodiac MX6 - July 2016 - Taylor K-2006 - Taylor K-1766 Salt Test

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    Re: Why Difference in Pool School Recommended CH Levels - Bleach vs SWG for Plaster P

    If a very negative CSI is corrosive, shouldn't I worry about that even if I have a vinyl liner? Or when you say it is corrosive, do you mean it is corrosive to plaster?

    I ask because in my pool (vinyl liner) I have let the CH level drop to around 120ppm and my CSI is like -.7. But I've tried to not let the bother me (even though it kind of does) because everything I've read says CH level (and thus CSI) don't matter with vinyl liner pools.

    But if my water is corrosive, that doesn't sound good for other things that touch the water, and I may want to adjust my chemicals to get my CSI back in line. I kind of like not having much CH though, the water is nice and soft.

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    Mod Squad pooldv's Avatar
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    Re: Why Difference in Pool School Recommended CH Levels - Bleach vs SWG for Plaster P

    It is only corrosive to plaster. As long as your pH is 7.2 or above you are fine. If it will make you feel better adding some CH won't hurt anything except for your time and money.
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    Re: Why Difference in Pool School Recommended CH Levels - Bleach vs SWG for Plaster P

    Cool. I am going to just try to get used to seeing a slightly out of whack CSI and ignoring it. As I said I do like having the softer feeling water. I just wanted to be sure I wasn't going to be eating up metal or anything else like that. Thanks for clarifying!

    17,500 gallon IG Vinyl
    Pentair Tagelus TA60D Sand filter
    Pentair Challenger 1.5HP pump CFII N1 1.5A
    Taylor K-2006-A, Stenner 45MPHP10 auto chlorine feed

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