Salt Concentration Measurement interpretation for SWG

[del]

First, I hope that I can actually ask this question in a somewhat coherent manner. I am wondering what gets measured when I go to the pool store and ask what my salt level is at. They are clearly just using something that measures conductivity that presumably all ions contribute to. Or, is it somehow actually measuring sodium chloride itself? I purchased a packaged home test kit for salt from Leslie's that tests for salts via a dip stick. Many times I get different results than what I get from the pool store via the conductivity meter. Do the dip sticks somehow just measure actual sodium chloride, or is it just measuring conductivity or total ion levels?

A follow up question involves my constant use of muriatic pool acid to reduce alkalinity. Presumably the acid reacts with the calcium carbonate (ionized) to create carbon dioxide and ionized Calcium Chloride. So, as this goes on for years on end, I assume that I end up with lots of ionized calcium chloride, in addition to the salt that I originally added for my SWG. Does this ionized calcium chloride just up as NaCl by either or both of the above mentioned tests? If the calcium chloride is part of the NaCl reading on the conductivity test, is that OK in terms of managing the level of "salt" in the pool for the SWG??? I am in San Diego, where we get lots of calcium hardness buildup over time as our city water is very hard.

I realize that I have asked a lot of questions all at once, but it may help me figure out something in terms of pool chemistry.

Del

 

[JoyfulNoise]

The best test kit for measuring salinity is the Taylor K-1766. It uses Mohr's method (argentometric titration) to measure the chloride ion (Cl-) concentration exactly and it is not interfered with by other ions (except for cyanide anion (CN-) which is not really present in pools). So, the K-1766 measures salinity very accurately and it is the number you should go by. All other methods are proxy measurements, either solution conductivity, capillarity or specific density, which are affected by other chemical species in the water.

Muriatic acid is hydrochloric acid or hydrogen chloride (HCl). It does not matter at all what the other counter-ions are in the reaction with carbonate alkalinity (HCO3-), as the chloride ion simply goes off into solution and adds to the salinity of the water. Depending on your pool volume and the acid concentration used, a gallon of MA can easily add 20-30ppm's to your chloride concentration. Any bleach or liquid chlorine used will also add slightly to your pool's chloride concentration. This is why we often tell people who scoff at SWG pool as being too corrosive to go and check their salinity, very often "non salt water pools" have just as much chloride salinity in them as salt-water pools

 

[pooldv]

A set of test results will help to see what's happening. There are different ways of measuring salt. But it is not particularly important what the number is as long as it is in the ballpark and your SWG is happy. If your SWG is making chlorine and not giving a hi/lo/salt error then it really does not matter that the salt "number" is. Most salt tests, including your SWG, are +/- 200-400 ppm. So, none is all that precise and give or take 500-1000 ppm is generally fine. I know that my SWG will work fine with salt anywhere from 2800 ppm to 4500 ppm.

SWGs do push pH up. A lower TA will help to offset that. Most folks find that TA between 50 and 70 is better to reduce pH rise.