Saturation Index

[DONNIE]

When using the Taylor WaterGram should I use my actual TA results or a CYA adjusted number? Should I even use the WaterGram or do the math myself?

Donnie

[chem geek]

You use the adjusted TA when you use the Taylor watergram. It comes out with almost exactly the same result as my spreadsheet which is more accurate than the traditional LSI so I think the watergram is great. On the other hand, you have to be pretty far out of balance before you get into a scaling or corrosion situation so don't sweat not being at "0.0" I wouldn't even have a second thought withing +/- 0.3 and most wouldn't care about +/- 0.5 and we have only started to see issues at 0.7 for one person and 1.0 for another.

This thread talks more about what people think about the index.

Richard

[DONNIE]

Thanks Richard. I assumed that would be correct but couldn't verify it. I'm glad to hear that you think the WaterGram is fairly accurate. You have always mentioned a corrosive property when refering to my water and after a little research I know what you are talking about. I'm well above -.5 and comfortable with that but always trying for perfection.

Donnie

[DONNIE]

would you please check the accuracy of this calculator when you get some spare time?

http://www.aquachek.com/calculators....lculator&CID=4

Thanks!!
Donnie

[waterbear]

pH is the most important factor, followed by temperature, in determining if water is going to be corrosive or scaling. Keep you pH in line and realize that the hotter the water the faster a chemical reaction (corrosion or scaling) will occur and you should be fine. If your calcium is through the roof then you might want to compensate by running your TA low but it's still the pH that is really going to determine if you have major problems or not. If you let it fluctuate or get out of range you will. If you keep tabs on it and keep it in line you will minimize the risk of problems.

[DONNIE]

Should I test for TDS? Wow! The Taylor K-1764 sells from $118 to $48 online.

Donnie

[chem geek]

Donnie,

I would not test for TDS. It takes a HUGE change in TDS to affect the saturation index so it is almost negligible. Besides, you can readily approximate your TDS by measuring the amount of chloride you have, which is measured using the Taylor K-1766 which is only $21.35. Most of your TDS is likely to be salt so measuring the chloride will give you a reasonable idea of your TDS -- not that it matters much anyway. Remember that the main chemical you are adding to your pool is chlorine and that this mostly gets converted to sodium chloride (if using chlorinating liquid or bleach) or calcium chloride (if using Cal-Hypo).

With normal levels of TA and CH and CYA, the amount of TDS is about 175-185 ppm more than the amount of ppm salt from the chloride test. This ignores organics that may stick around in your pool and assumes no sulfates, but that's usually a reasonable assumption. My spreadsheet will calculate this relationship between measured chloride (as ppm sodium chloride) and TDS assuming that there is nothing in the water except what you list as coming from CH, TA and CYA and sulfates (and FC, but that's very minor).

Richard

[chem geek]

would you please check the accuracy of this calculator when you get some spare time?

http://www.aquachek.com/calculators....lculator&CID=4

Thanks!!
Donnie

I get somewhat different results, especially at higher temperatures such as those found in a spa (about 0.2 units different). The differences are small at normal temperatures -- within 0.1 units. Again, I wouldn't worry about such small differences. If you want an accurate calculator that pretty much matches the Taylor watergram (except for the highest temperatures well above spa temperatures where it is off by 0.1), then go to the end of the first post in this thread and download my spreadsheet in the PoolEquations.zip file. It calculates both the traditional LSI as well as the more accurate one that matches the Taylor watergram.

Richard

[DONNIE]

So I don't need to include TDS in the saturation index or do I use my 3600 ppm salt?

[chem geek]

So I don't need to include TDS in the saturation index or do I use my 3600 ppm salt?

You should include it in the index, using say 3800 ppm (200 ppm more than the salt measurement), but don't bother measuring TDS explicitly.