Pool Math and CSI dont jive.

Jan 23, 2019
9
Houston, Texas
#1
I'm converting to SWG (ichlor30.) Pool is 16500 gallon pebbletech. When I play with the calculations entering variations of the recommended targets for SWG pool I'm getting like -5 which CSI says anything lower than -3 is corrosive. I've adjusted every target within the ranges recommended and cant get close to balanced. What am I missing?
 
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dja2477
Jan 23, 2019
9
Houston, Texas
#3
Left column is what is suggested and the right column is my water now. I guess this method relays heavily on keeping CH at near 400 and pH at higher range at 7.7-7.8. I'm just curious why this is a better method for SWG pool.

Recommended / Actual
FC 5 / 7
pH 7.6 / 7.7
TA 70 / 95
CH 350/ 275
CYA 70 / 35
Temp 63 /63
Salt 3800 / 3800
Bor 40 / 30
CSI -.48 / .16
 
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duraleigh

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#4
I am not a fan of CSI and this is an example. It is far more important to know and understand why CH of 400 is NOT good for your pool rather than plugging in a math calculation and following it blindly.

Someone will help you sort out the math error but I can tell you a CH of 400 is not suggested for a pool.
 
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Texas Splash

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#5
DJA, I ran your numbers in Poolmath and I'm getting a CSI of -0.26. Not sure about the -0.5 you saw. So it looks like you are sitting well. As for the recommended levels you noted, you have room to the left/right for each parameter which can help bring your CSI closer to neutral if you're really worried about it. You can view those levels on the Recommended Levels page. Water temp is our biggest challenge this time of year, and that won't be an issue soon. If your local water is hard, your CH should climb back to the 350 (minimum) this season, So you can wait on that and simply let your pH and/or TA ride a little higher to compensate, or simple add a little calcium. But if you do add calcium, I would shoot for the minimum 350 range. Don't go too high or you'll have a higher CH than you need. And as soon as your water temp gets back to the 80 range, your CSI will climb very fast. As Dave noted, CSI has it's applicability, but we are careful to not get too wrapped around the axle on it. As long as you keep your numbers in those recommended ranges you should be fine. Lastly, please show which city you are from in Texas. As you know, the weather impact on pools varies from N, S, E & West.
More about CSI here: Calcium Saturation Index
 
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dja2477
Jan 23, 2019
9
Houston, Texas
#6
I agree that much calcium seems too high but that is whats suggested. You can make the numbers work to get a good CSI however the ranges required are not what I'm used with a freshwater pool. And the CYA at required 70 or 80 almost makes me cringe because I just drained my pool to get rid of high cya. The main reason I decided to go with a swg was to stop the cya problem of trichlor and having to drain. . Now here I am about to dump a bunch back the pool. A bit ironic.
 
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dja2477
Jan 23, 2019
9
Houston, Texas
#7
DJA, I ran your numbers in Poolmath and I'm getting a CSI of -0.26. Not sure about the -0.5 you saw. So it looks like you are sitting well. As for the recommended levels you noted, you have room to the left/right for each parameter which can help bring your CSI closer to neutral if you're really worried about it. You can view those levels on the Recommended Levels page. Water temp is our biggest challenge this time of year, and that won't be an issue soon. If your local water is hard, your CH should climb back to the 350 (minimum) this season, So you can wait on that and simply let your pH and/or TA ride a little higher to compensate, or simple add a little calcium. But if you do add calcium, I would shoot for the minimum 350 range. Don't go too high or you'll have a higher CH than you need. And as soon as your water temp gets back to the 80 range, your CSI will climb very fast. As Dave noted, CSI has it's applicability, but we are careful to not get too wrapped around the axle on it. As long as you keep your numbers in those recommended ranges you should be fine. Lastly, please show which city you are from in Texas. As you know, the weather impact on pools varies from N, S, E & West.
More about CSI here: Calcium Saturation Index
Ok, Ill try not to let the numbers eat at me. Im in Houston so the heat is coming soon and I know that will help a lot. I was just concerned about the high calcium. I don't like it. I'll bring it to 350 and adjust accordingly but refuse to dump another 10 or 15 pounds of calcium in my pool.
 

Texas Splash

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#8
I'll bring it to 350 and adjust accordingly but refuse to dump another 10 or 15 pounds of calcium in my pool.
I don't blame you. It adds-up fast in our area as well. I think you're in good shape, and our water temp is beginning to climb, so I suspect your CSI will look much different in the coming weeks. It takes many months of a very negative (or positive) CSI to really make an impact anyways. Enjoy the weekend and get ready for another season. :swim:
 
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ping

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Jun 24, 2011
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Long Beach, CA
#9
Please post your fill water test results for TA, pH, and CH before adding anything other than CYA to the pool. You might regret adding calcium if your fill water will be raising it.
 

Arizonarob

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#13
And the CYA at required 70 or 80 almost makes me cringe because I just drained my pool to get rid of high cya. The main reason I decided to go with a swg was to stop the cya problem of trichlor and having to drain. . Now here I am about to dump a bunch back the pool. A bit ironic.
Dj, the main reason you need to keep you CYA in the 70-80 range with a SWG, is to offer the chlorine being produced some sunscreen. If you were to continue keeping it at your current level, you will find yourself having to crank up your % output to compensate for the rapid burn off.

Now that you have a SWG, you no longer have to worry about climbing CYA levels from using pucks. In fact, over the course of the summer your CYA levels will begin to drop, due to oxidation of it from the Sun.

To give you an example, I do not have a SWG but yet I keep my CYA at 80. Here in AZ the summer is HOT, and the sun is strong. Beginning in April I raise my CYA up to 80, and come September it has fallen to 40, where it currently sits.
Hope this helps. :cheers:
 
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dja2477
Jan 23, 2019
9
Houston, Texas
#18
As an operator for Shell Oil making gas, running samples and controlling the process is built in and following me home. I''l try to ease up a bit. Thanks for the input.
 

duraleigh

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#19
So, if you intend to take your CH to 350, I think that is a mistake. I think we have a flaw in our posted suggestions and I would NEVER add CH to that pool.

CH never goes away. It ONLY increases as you add fill water of 175 to the existing CH in your pool. You will be well over 500 in the middle of swim season and then your only recourse will be drain and refill.

Again, CSI is only a math calculation for the tendency for calcium scale. To rely on it as a valid parameter is a tempting crutch but you will be far better served if you ask more questions, read further and understand the range of CH available to you and the consequences.
 
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