A Salt & Calcium Question...

[Russmd]

I've been having a quandry with my salt pool's salt levels steadily rising without the addition of any exogenous salt by me. Testing is with the Taylor 1766 kit. Recently it was up to around 4400. I drained roughly 1/3 of the water, refilled, and it tested at 2800. It's been 4 weeks since then and it's now at 3200. A few items to consider in the mix: I live in SoCal where it's very hot and there's a lot of evaporation. Our fill water source is VERY hard and used to give me terrible scale on the pool and cell, so I put an exchange water softener on the inflow to take out some of the calcium. That works pretty well. I know that may add salt by exchange but I tested the softened infow water (300ppm) and non-softened inflow water (250-300ppm) so not too different per my test kits. I know this is not as precise as one might like but would the possibly slightly higher Na inflow of softened water significantly account for my real rising sodium levels? (say when the exchange tank is new and resin is full of salt). If I don't use the softener, calcium goes through the roof and destroys my tile, cell, and pipes. I'm in a quandry between these two items - Na and Ca - and short of water replacements, can't figure a solution.
(Even trying that Jacuzzi electonic RF calcium descaler thing but don't have high hopes for it - money back guarantee). Thanks,
Russ

 

[mknauss]

That is odd. There are several members here that use a softened water for the pool and have no rising salt issues. My salt level goes up slightly over time but not anywhere near as fast as what you are showing.

Let's see if @JoyfulNoise has any thoughts on this.

 

[Russmd]

Thanks, I agree it is odd. Many people here describe splashing and playing causing (salt) water loss. No kids at home anymore, no splashing and playing. Cell takes care of chlorine just fine. Because of the high Ca, does require a fair amount of muriatic acid to keep pH 7.8 or less to keep CSI down. Acid?

 

[JamesW]

Acid raises the salt level.

 

[mknauss]

Acid adds salt. But not that much. The pH rises because your TA rises from the fill water.

 

[JamesW]

Every gallon of acid contains about 2.92 lbs of chloride, which equates to about 4.81 lbs of salt per gallon.

 

[JoyfulNoise]

So the K-1766 chemically measures chloride ion (Cl-) ion content and the units are reported in terms of “ppm of NaCl” under the assumption that most of the chloride in your pool is derived from adding pool salt. That’s typically a good assumption.

Anything with chlorine in it will eventually raise the chloride ion concentration over time.

Water softeners that use ion exchange resins and salt for regeneration will NOT add any excess chloride ion to your water. The exchange is sodium for calcium and the chloride is only present when the system is regenerating. After regeneration, a good water softener goes through a backwash and rinse cycle to remove any excess brine. If you are getting any increase in chloride from the softener, it’s not working properly.

 

[Russmd]

My softener is an exchange resin tank switched out on a schedule. I don’t add salt or backwash it.

 

[JoyfulNoise]

My softener is an exchange resin tank switched out on a schedule. I don’t add salt or backwash it.

Those types are still sodium ion exchange resins, it’s just that someone else does the regenerating. Either way, it will not raise chloride ion content nor will it affect the K-1766 test.

 

[Russmd]

Fascinating, thanks. So the K-1766 is actually measuring chloride ion, good to know. The "salt" number reported by my salt cell also rises in accordance with the K-1766 number.
-Do the salt cell electronics also measure chloride ion then?
-If so, taking it one step further, what is adding Cl- to my pool? All I can think of then in the muriatic (HCl) acid as mentioned before.
If all those are true, then I'm not sure what else I can/should do differently. My TA is around 70. I like to keep the pH no higher than 7.8 because with the high Calcium, my CSI would get too high causing cell and scaling problems. I have 50ppm borates. Dry acid would add sodium and sulfates bring their own problems.. Any other ideas to keep things balanced and within good ranges?
Thanks.

 

[JoyfulNoise]

Fascinating, thanks. So the K-1766 is actually measuring chloride ion, good to know. The "salt" number reported by my salt cell also rises in accordance with the K-1766 number.
-Do the salt cell electronics also measure chloride ion then?
-If so, taking it one step further, what is adding Cl- to my pool? All I can think of then in the muriatic (HCl) acid as mentioned before.
If all those are true, then I'm not sure what else I can/should do differently. My TA is around 70. I like to keep the pH no higher than 7.8 because with the high Calcium, my CSI would get too high causing cell and scaling problems. I have 50ppm borates. Dry acid would add sodium and sulfates bring their own problems.. Any other ideas to keep things balanced and within good ranges?
Thanks.

SWG cells measure the electrical conductivity (EC) of the water and then “infer” a salt level from that. That method is inherently inaccurate and an SWG readout will never be better than +/-400ppm. The K-1766 is 200ppm per drop but one can simply double the sample size (20mL) and get +/-100ppm per drop.

What does your municipal water supply measure at for chloride ion concentration ? You can test your fill water with your K-1766 to get a sense of it. If you know your evaporation rate you can add that amount to any known chloride sources (line muriatic acid) to see if it accounts correctly.

 

[Russmd]

Thanks so much. I was ahead of you on the municipal supply readings: using the K-1766, I got 300ppm from both the untreated municipal supply (irrigation spigot) as well as the outflow after the resin exchange softener. I have no idea how to figure evaporation rate other than to say it's probably quite high. It's hot here in Southern California, especially now. I also have a spillover from the spa into the pool which causes quite a bit of aeration (which if I understand it correctly, releases CO2 and drives pH up. Therefore, we use quite a it of acid - probably a half-gallon a week - to keep it at 7.7. TA is now 70. CYA 50. BTW, the softener supply water has a pH of 7.5 and Calcium of 40 (untreated Ca is 350). I was considering adding the appropriate amount of acid to get my TA down a little, maybe to 60 - may decrease the amount of acid I'll need to add in the future?
Russ

 

[JoyfulNoise]

Measuring 300ppm [NaCl] in your municipal supply equates to a chloride ion concentration of ~ 182ppm [Cl-] .... that is well below any known health effects. It also sets an upper bound to your evaporation effect - even if you evaporated your entire pool volume in one season (which we do here in Tucson), you’d only see an increase in chloride of ~180ppm. So your fill water is not a substantial contributor. Every gallon of acid added to your pool will increase the measures sodium chloride levels by ~19ppm, so that is a decent source of chloride. The K-1766 test is +\- 100ppm easily so you’re probably just seeing the effect of all the acid you are adding.

Decreasing TA and aeration will decrease acid demand. Best to look into that.

 

[Russmd]

Thank you so much! Makes good sense. I expect as much from a fellow Tucsonan- I was born and raised in the Old Pueblo, left after undergrad at U of A. You see what my minor in chemistry from there got me . Hopefully a lower TA will let me cut down on muriatic acid. I probably can guess, but what are your feelings on using dry acid, even sparingly?

 

[JoyfulNoise]

With an SWG (or plaster for that matter) you want to avoid adding sulfates your your pool. Dry acid is simply sodium bisulfate and sulfates will attack the catalytic metal coating on the SWG plates shortening their lifespan. Cementitious materials can suffer from “sulfate attack” which weakens them.

If you have leftover dry acid and don’t want to throw it away, use it in your garden. You can lower the pH of irrigation water as plants appreciate lower pH (~6.5 to 7) while soil bacteria can utilize the sulfates.