Saturation index

ethany

LifeTime Supporter
May 23, 2009
528
Trenton NJ
I'm reading my pool Pilot Dig-220 manual and came across the way to figure out your SI. It says :

Ph 7.4 + water temp(76degrees) 0.6+ CH (250) 2.0+ TA(80) 1.9 - salt level (3500) 12.4 = SI of -.5

Is that too high? It says it's ok if between -.3 thru .3

If so how can I adjust to an acceptable level.
 

pooldv

TFP Expert
Platinum Supporter
LifeTime Supporter
Moderator Emeritus
Aug 10, 2012
25,412
FL panhandle
-0.5 is fine for a fiberglass pool, negative SI is not a problem for FG, only plaster. To raise the SI you can raise PH a bit. PoolMath, link at top of page, will also calculate your CSI when you winter all your test results.

More about scale and etching here, Pool School - Calcium Scaling
 

needsajet

TFP Expert
LifeTime Supporter
Jan 4, 2016
4,752
Sydney, NSW, Australia
Pool Size
44000
Surface
Plaster
Chlorine
Salt Water Generator
With TFPC you can use PoolMath (button at the top) to calculate your calcite saturation index. It's a bit better than the Langelier saturation index, which is probably the one you'll find in your manual.

I entered your numbers in PoolMath, and used 40 for CYA (which you would need to change to the correct number) and got around -0.5 as well, so yes, it's a bit too low. Let your pH drift up to between 7.5 and 7.8 and you'll have a less aggressive CSI. You could also do with a bit more CH, which is raised with calcium chloride. I can't tell where you live, but many water supplies will add CH over time, so consider that as well, and when you get a chance, add your location.

Overall your numbers don't look bad, but it would be helpful to see the CYA level.
 

ethany

LifeTime Supporter
May 23, 2009
528
Trenton NJ
Ok thank you.... the reason I keep the ph a little low is I've had problems with stains in the past. I thought I read somewhere to keep the ph around 7.2/7.4ish
 
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