Saturation index

[ethany]

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]

-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]

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]

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

 

[pooldv]

Yes, keeping pH 7.2 to 7.4 can help prevent staining.

 

[needsajet]

Whoops, sorry I missed that you have fiberglass! pooldv has you covered.