CSI calculation

[nak]

Since I was using calcium hypochlorite to do my shocking, and shocking ~1x/week, I am interested (and slightly concerned about) in my CH level (even though I know for vinyl pools the CH isn't critical). Although still waiting for my TF-100 kit in the mail, I took a sample to the pool store and they told me I'm at 450 ppm Ca2+ (not surprising). When I plug the pool store values into the CSI calculator in the Pool Calculator I get CSI = -0.57.

In the description it says "Less than -0.6 is suggestive of problems for plaster, tile, stone, and pebble pools. Greater than 0.6 is suggestive of problems for all pools." Does that actually mean LESS than -0.06 is suggestive of problems? So -0.8 is suggestive of problems for plaster/tile/stone/pebble? Or less negative, meaning the range from <-0.6 is the ideal zone, -0.6 to 0.6 is the risky zone and >0.6 is the danger zone?

I assume I want my CSI to be as low as possible? When I play around with the numbers it seems to be this way, but the wording in that description leads me to think otherwise.

 

[Vette]

Well in a vinyl pool, low CH doesn't matter. In other pools, low CH can cause the plaster and other substances to pit due to the water needing to satisfy its appetite for CH. In any pool including vinyl, too high CH can cause calcium scaling. Some people deal really well with high CH, Richard is one who has super high CH water but keeps it in check by keeping a close eye on PH. I would wait for your TF100 before making any judgements based on test results. If you have no calcium scaling, you are fine for now.

 

[JasonLion]

Most people never need to think about CSI at all. As long as you follow our recommended levels you will be fine. Nominally, anything from -0.6 to +0.6 is fine, though you need to be careful as you near the upper end of that range. Lower than -0.6 can cause problems for plaster/tile/pebble/quartz pools. Higher than 0.6 can cause problems for any kind of pool.

 

[chem geek]

The unit of measurement for Calcium Hardness (CH) is ppm CaCO₃, not ppm Ca²⁺ so did they give you the right number? Also, only with a pH of 7.2, TA of 70 ppm, Temp of 80ºF, CYA of 80 ppm, 3000 ppm salt, do I get a CSI of -0.55 so does your pool have high salt levels and a low pH and TA? Though a low CSI isn't an issue for vinyl pools, I'm more concerned with what your other water parameters actually are. Also, I would not trust pool store results at all. I know it's hard to get a good test kit in Canada and that the Taylor K-2006 is more expensive there. Can you please post the full set of test results you have and used in The Pool Calculator?

 

[jblizzle]

I too wonder about your other levels as that is a pretty low CSI with the higher CH. I am guessing this is due to a low pH, which has the largest affect on CSI.

Posted from my Droid with Tapatalk ... sorry if my response is short

 

[nak]

The unit of measurement for Calcium Hardness (CH) is ppm CaCO₃, not ppm Ca²⁺ so did they give you the right number? Also, only with a pH of 7.2, TA of 70 ppm, Temp of 80ºF, CYA of 80 ppm, 3000 ppm salt, do I get a CSI of -0.55 so does your pool have high salt levels and a low pH and TA? Though a low CSI isn't an issue for vinyl pools, I'm more concerned with what your other water parameters actually are. Also, I would not trust pool store results at all. I know it's hard to get a good test kit in Canada and that the Taylor K-2006 is more expensive there. Can you please post the full set of test results you have and used in The Pool Calculator?

Yes, but what does CaCO3 become when it dissociates in water? Ca2+ and (CO3)2-. Regardless, they didn't give units for CH, just "Hardness = 450 ppm".

My TF-100 kit is in the mail so at the moment all I have to go off of is the pool store results. For my calculation in the Pool Calculator I used:
FC 2.2
pH 7.0
TA 70
CH 450
CYA 100
salt 0
borate 0 (salt and borate weren't tested for, and I'm not using a SWG so presumably the Na+ will be low)

Should I be entering different values for salt/borate? I didn't think a value of -0.57 was unreasonable, but it did seem more "normal" than I was expecting for a hardness of 450 ppm.

 

[Vette]

Well you probably have some salt, maybe 100 or so, but that won't change your result much. Really, CSI isn't something to stress over.

 

[jblizzle]

The pH of 7 is the largest driver. That is lower than we normally recommend which is a minimum of 7.2

Posted from my Droid with Tapatalk ... sorry if my response is short

 

[chem geek]

It's a vinyl pool so as we said, the low CSI doesn't matter. Low pH isn't good for vinyl (or metals), however. 7.0 isn't horrible, but there's really no reason to keep it that low and getting it into normal range at 7.2-7.8 would be better. The Pool Calculator will use a minimum presumed salt value implied from the TA and CH levels so don't worry about entering in 0 for that (and a low salt or TDS level doesn't affect the CSI much anyway -- it's mostly higher levels such as for saltwater chlorine generator pools where it starts to have a more significant effect, though still not huge). If your Total Hardness is 450 ppm then your Calcium Hardness (CH) is probably around 300 ppm since most of total hardness is usually calcium with the rest being magnesium. The units of measurement for both hardness values is ppm calcium carbonate.