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Thread: 2 Questions....CSI in Pool Calculator and CC

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    hawkeyes's Avatar
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    2 Questions....CSI in Pool Calculator and CC

    I have 2 questions:

    1. Does CC show up overnight if you have algae/organics? I did a chlorine test last night around 9 pm. I got a reading of 5 and absolutely no cc. This morning (I got busy and forgot so the sun had been on the pool about 90 min. Equipment had not yet kicked on) and the reading is 4.0 and .5.

    2. CSI. When I put all my numbers in the pool calcuator, everything appears to be balanced according to my target but the CSI shows "potential to become corrosive to plaster". Everything I have been targeting is dead on so I'm confused. In fact, I usually shoot for a pH of 7.3 or 7.4 b/c I know it rises quickly. Today is 7.5 and the lower I take my pH in the target column the worse the CSI becomes. My CH is high but the HIGHER I put that target column the BETTER my CSI becomes. I'm confused. I definitely don't want to target a higher pH due to scaling potential. At low CSI what is the risk? The articles I find on CSI are for chemistry majors (of which I was not). Should I just not worry about this number right now and focus on keeping my pH and TA in check?


    TC 4.5
    pH 7.5
    CH: 370
    TA: 70
    CYA: 70
    Salt 3200
    Temp 86
    22,000 gal IG Pool & Spa, Fountain and Spa Spillway, Penatair IC-40 SWCG, Pentair Intelliflo Variable Speed Pump, Cartridge, Antigua Blue Wet-Edge

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    billybrobob's Avatar
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    Re: 2 Questions....CSI in Pool Calculator and CC

    Keep doing what you are doing.
    40,000 gal pool, Goldline SWG, 1.5 hp pump, sand filter, plaster w/epoxy paint.

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    Re: 2 Questions....CSI in Pool Calculator and CC

    "Potential to become corrosive to plaster" does not mean that it IS corrosive to plaster. You just need to be watchful is all.

    Your CSI is -0.3 and this is not worrisome per se. We usually recommend keeping the CSI a tad bit negative anyway. One of the benefits of the Pool Calculator is that it affords the user the ability to play with the numbers a bit to achieve optimum balance. By using your numbers, I can tell that your CSI looks a little better with the pH on the higher side, say 7.6. Dropping the pH to around 7.2 gets your CSI really close to -0.6 and you don't want to be beyond that.

    Now, if you run some tests and you discover one day that your CSI is beyond the recommended range one way or the other, all is not lost so don't panic. Just play with the numbers and adjust the things that are the easiest to adjust (pH and TA for example). Then, you can get it right. An out of range CSI for a few days will not cause your pool to implode or anything . All CSI is is an indicator of scaling or corrosion potential and scaling or corrosion are things that take a little time to happen.

    All in all, you are fine right now.

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    hawkeyes's Avatar
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    Re: 2 Questions....CSI in Pool Calculator and CC

    Quote Originally Posted by 257WbyMag
    "Potential to become corrosive to plaster" does not mean that it IS corrosive to plaster. You just need to be watchful is all.

    Your CSI is -0.3 and this is not worrisome per se. We usually recommend keeping the CSI a tad bit negative anyway. One of the benefits of the Pool Calculator is that it affords the user the ability to play with the numbers a bit to achieve optimum balance. By using your numbers, I can tell that your CSI looks a little better with the pH on the higher side, say 7.6. Dropping the pH to around 7.2 gets your CSI really close to -0.6 and you don't want to be beyond that.

    Now, if you run some tests and you discover one day that your CSI is beyond the recommended range one way or the other, all is not lost so don't panic. Just play with the numbers and adjust the things that are the easiest to adjust (pH and TA for example). Then, you can get it right. An out of range CSI for a few days will not cause your pool to implode or anything . All CSI is is an indicator of scaling or corrosion potential and scaling or corrosion are things that take a little time to happen.

    All in all, you are fine right now.

    Is a HIGH CSI number conducive to scale and LOW CSI conducive to corrosion of plaster, equipment, etc? Keeping my pH on the "higher side" (anything 7.6 and up is high to me b/c I am PARANOID about scale---esp given my high CH) freaks me out and goes against the motto that has been in my head for 3 months now....."Keep pH down, Keep pH down, Keep pH down".
    22,000 gal IG Pool & Spa, Fountain and Spa Spillway, Penatair IC-40 SWCG, Pentair Intelliflo Variable Speed Pump, Cartridge, Antigua Blue Wet-Edge

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    Re: 2 Questions....CSI in Pool Calculator and CC

    Yes, high CSI = scale and low CSI = corrosion.

    Your CH, although not terribly high or anything, is higher than recommended. But the simple fact that you know this and understand the concepts behind it bodes well for your situation.

    There are people here who must contend with very high CH due to the presence of calcium in their fill water. They have found that by watching their CSI closely, they can manage their pools pretty well by making other adjustments (pH and TA) to account for the high CH and be scaling free as a result. You can operate a pool with very high CH levels by watching CSI.

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    Re: 2 Questions....CSI in Pool Calculator and CC

    Quote Originally Posted by 257WbyMag
    Yes, high CSI = scale and low CSI = corrosion.

    Your CH, although not terribly high or anything, is higher than recommended. But the simple fact that you know this and understand the concepts behind it bodes well for your situation.

    There are people here who must contend with very high CH due to the presence of calcium in their fill water. They have found that by watching their CSI closely, they can manage their pools pretty well by making other adjustments (pH and TA) to account for the high CH and be scaling free as a result. You can operate a pool with very high CH levels by watching CSI.
    Ok....so maybe by knowing I have high CH I need to target more of a 7.6 pH instead of 7.4? I had previously been working hard to get my pH to 7.3-7.5 and TA lowered to around 70. I need to test my fill water for CH myself as I've only had Leslie's do it and I don't trust them for **** since they tell me my CYA is 25 and I swear it is closer to 65/70.

    ETA: Fill water is 190 CH. How can I go from 190 to 380?
    22,000 gal IG Pool & Spa, Fountain and Spa Spillway, Penatair IC-40 SWCG, Pentair Intelliflo Variable Speed Pump, Cartridge, Antigua Blue Wet-Edge

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    Re: 2 Questions....CSI in Pool Calculator and CC

    I think I am a little confused as to what you are trying to avoid. Just so we're on the same page:

    As pH, TA, CH go up, CSI goes up.
    As ph, TA, CH go down, CSI goes down.

    Salt, temperature, borates contribute to CSI, but they are not really anything you would tweak to adjust your CSI.

    High CSI: Scaling, cloudy water.
    Low CSI: Corrosion to plaster.

    Your numbers really look great. I would have no concern on either end of the scale.

    Now, if you came here with a DOUBLE TA and DOUBLE CH, I would probably suggest you target a pH of around 7.2 at least until you get your TA down.

    If you came here with HALF your TA and HALF your CH, I would probably suggest adding some baking soda and calcium be added, and keeping your pH 7.5... 7.6 until TA and CH gets in line. But still... no need to panic.

    Where your numbers are, I would only be responding to problems: Is your pH bouncing, or drifting, are you getting scaling, or cloudiness? If not I don't think you have any worries.

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    Re: 2 Questions....CSI in Pool Calculator and CC

    If your fill water is 190, then your CH will rise as you top it off. On a fresh fill, you will start with a CH of 190. Over time, water evaporates. This means that water leaves the pool but the calcium stays behind. You top it off with tap water which adds more calcium. The process repeats itself.

    Evaporating water never takes the dissolved substances with it. Kinda like putting a pot of water on the stove and boiling it dry. You can see the minerals left behind in the pot as scale. Only the water left.

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    Re: 2 Questions....CSI in Pool Calculator and CC

    Quote Originally Posted by waskydiver
    I think I am a little confused as to what you are trying to avoid. Just so we're on the same page:

    As pH, TA, CH go up, CSI goes up.
    As ph, TA, CH go down, CSI goes down.

    Salt, temperature, borates contribute to CSI, but they are not really anything you would tweak to adjust your CSI.

    High CSI: Scaling, cloudy water.
    Low CSI: Corrosion to plaster.

    Your numbers really look great. I would have no concern on either end of the scale.

    Now, if you came here with a DOUBLE TA and DOUBLE CH, I would probably suggest you target a pH of around 7.2 at least until you get your TA down.


    If you came here with HALF your TA and HALF your CH, I would probably suggest adding some baking soda and calcium be added, and keeping your pH 7.5... 7.6 until TA and CH gets in line. But still... no need to panic.

    Where your numbers are, I would only be responding to problems: Is your pH bouncing, or drifting, are you getting scaling, or cloudiness? If not I don't think you have any worries.

    Water is a tad cloudy but nothing bad. Scaling is my biggest concern b/c it has already happened once and I'm paranoid about it. No one believed me last time when I said I was seeing a film of "white/grey" form over the pebble tec and, being a new pool owner, I really was clueless. By the time someone listened to me, they had to do a drain and acid wash. So my question was really only about targeting a lower pH like I have been to avoid the scaling (7.4-ish) compared to that causing the CSI number to be pretty low. Sounds like all is fine and I just need to stop worrying/obcessing about it.

    Yes my pH constantly drifts up---every other day I add a fair amount of acid. It is a new pool so I am hoping that will subside in time.

    CH explanation: Yep...I remember someone explaining that to me now. CH doesn't evaporate so every time I top off my pool (which is a LOT right now due to hot temps and lots of kids in pool causing splash out) it adds more calcium. Dreaded cycle.
    22,000 gal IG Pool & Spa, Fountain and Spa Spillway, Penatair IC-40 SWCG, Pentair Intelliflo Variable Speed Pump, Cartridge, Antigua Blue Wet-Edge

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    Re: 2 Questions....CSI in Pool Calculator and CC

    OK... I think I get it...

    I think that targetting a 7.4 would give you a pretty good margin in your CSI. Plus, you would have a tendency towards a lower TA with the acid additions you would need to keep it there. This lower TA would further lower your CSI.

    Problem would be that with the lower TA, your pH would be pretty sensitive. To counteract that a bit, you could add some borates. Borates will help you as 1) They will provide additional buffer for your pH, without quite as much effect on your CSI as TA. 2) It will provide more algea control, so, your SWG may not have to work as hard, which could mean less upward swing of your pH.

    I still do not think that you should have much to be concerned about, but aiming for a 7.4, and adding some borates wouldn't hurt anything. But, I cannot predict exactly how this is going to work. We are kinda in the fine-tuning range here, and things get a little harder to predict. If making changes like this, I would check your TA a little closer. You may need to do a little small changes there to rediscover your sweetspot.

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    hawkeyes's Avatar
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    Re: 2 Questions....CSI in Pool Calculator and CC

    Quote Originally Posted by waskydiver
    OK... I think I get it...

    I think that targetting a 7.4 would give you a pretty good margin in your CSI. Plus, you would have a tendency towards a lower TA with the acid additions you would need to keep it there. This lower TA would further lower your CSI.

    Problem would be that with the lower TA, your pH would be pretty sensitive. To counteract that a bit, you could add some borates. Borates will help you as 1) They will provide additional buffer for your pH, without quite as much effect on your CSI as TA. 2) It will provide more algea control, so, your SWG may not have to work as hard, which could mean less upward swing of your pH.

    I still do not think that you should have much to be concerned about, but aiming for a 7.4, and adding some borates wouldn't hurt anything. But, I cannot predict exactly how this is going to work. We are kinda in the fine-tuning range here, and things get a little harder to predict. If making changes like this, I would check your TA a little closer. You may need to do a little small changes there to rediscover your sweetspot.
    I have considered adding Borates but was afraid I was biting off more than I could chew since I'm just now feeling like I'm getting a handle on my water balance. I didn't want to add another chemistry to the mix since I tend to overwhelm easily.

    Thanks for your help.
    22,000 gal IG Pool & Spa, Fountain and Spa Spillway, Penatair IC-40 SWCG, Pentair Intelliflo Variable Speed Pump, Cartridge, Antigua Blue Wet-Edge

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