Saturation Index

Jump to latest Follow Reply
J

Jessica K

0
Jul 12, 2016
12
Atlanta, GA
Hi folks. I had my pool replastered with Wet Edge pebble finish a few weeks ago. I thought I had finally got all my of chemistry values right where I wanted them. Readings from today:
FC=8
TC=8
PH=7.4
CH=260
TA=80
CYA=30

So everything is within the recommended ranges. But, I just used Taylor's water balance calculator (the fun little wheel that comes with the test kit), and with these values and a pool temp of about 70 degrees F, the saturation index is -0.25. It says -0.3 or lower is corrosive. Is a SI of 0 best, or are you okay as long as you are within the range of -0.3 to 0.5?

Are there any parameters I should adjust to get it closer to zero? Assuming I want to stay at PH of 7.4 and I can't change the water temp, I gather that I would have to raise CH and TA.

Also, I read somewhere online that for exposed aggregate pools, ideal CH is between 200 and 250 (lower end of range). Anyone ever heard of that? Is that right?
 
If you use Pool Math, TFP bases it's saturation index recommendations on the calcite saturation index (CSI) which is a little different in it's calculation than the modified Langlier Saturation Index (LSI) that Taylor uses. The CSI is more applicable to pools as it is directly related to calcium carbonate saturation and takes into account all relevant parameters.

Your CSI as it currently stands is about -0.32 which is only very slightly above what we recommend (between -0.3 and +0.3 is OK). Your biggest driver of saturation is going to be pH with TA be next biggest lever you can adjust. If you simply allow your pH to rise to 7.8, then your CSI will go right to 0. There is no need to keep your pH so low (yes, for most pools, 7.4 is a little low). Pool water is comfortable and safe for humans and equipment anywhere between 7.2 and 7.8, so targeting 7.4 is really unnecessary. Typically, allowing the pool water to float between 7.6 and 7.8 (that is, only adding acid to lower pH when it goes above 7.8 and then, only adding enough to lower it to 7.6) is more than adequate.

I would not change your CH. CH naturally rises over time unless you have significant amounts of rainwater (freshwater) exchange. 260ppm is fine for plaster and I would only think about increasing it if you find your CH down near 200ppm.

With all that said, since your plaster is new and under warranty from your applicator, you need to follow their recommendations on water chemistry in order to NOT VIOLATE YOUR WARRANTY. All plasterers are different in this regard but some do require PROOF of water balance from a third party testing company (like a pool store) in case you need to make a warranty claim. So if that situation applies to you, then you need to follow their recommended saturation levels.
 
Thanks, Pooldv...I hadn't used the pool calculator in a while and forgot it calculated saturation. And thanks joyful noise for explanation of CSI vs LSI, had no idea. Good to know about pH too. I am thinking the curing of new plaster will drive it back up soonish, and CSI of zero should be easier to attain with a pH between 7.6 and 7.8. That is where my water tended to sit pre-renovation, and it was always fairly easy to balance.
 
My new pebblesheen surface is drinking acid, I am on my 6th jug in two weeks. Looks beautiful though, got home last night pH 7.8, add acid. Kindof a routine, get it to 7.2 and a day or two later 7.8.

Jessica K said:
Thanks, Pooldv...I hadn't used the pool calculator in a while and forgot it calculated saturation. And thanks joyful noise for explanation of CSI vs LSI, had no idea. Good to know about pH too. I am thinking the curing of new plaster will drive it back up soonish, and CSI of zero should be easier to attain with a pH between 7.6 and 7.8. That is where my water tended to sit pre-renovation, and it was always fairly easy to balance.
Click to expand...
 
PebblePool said:
My new pebblesheen surface is drinking acid, I am on my 6th jug in two weeks. Looks beautiful though, got home last night pH 7.8, add acid. Kindof a routine, get it to 7.2 and a day or two later 7.8.
Click to expand...

Why are you dropping the pH so low? It's usually not necessary to do that and typically leads to greater acid use.
 
You must log in or register to reply here.
Thread Status
Hello , This thread has been inactive for over 60 days. New postings here are unlikely to be seen or responded to by other members. For better visibility, consider Starting A New Thread.
Top Bottom
Back
Jump to latest Follow Reply