Why doesn't a salt pool require additional salt?

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texasmax

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May 24, 2010
202
Dallas, TX
Getting ready to start new construction, and going with a salt system for the first time. Everything I'm reading says to get the salt concentration to the appropriate level, and then you don't generally need to add any (outside of splash out). Is the salt usage extremely low in providing the FAC to the water? Or is there something else going on? There's no infinite regeneration loop here- FAC gets used, and I don't see the byproducts getting tuned into useable product. Unless, the salt cell is not only providing electrolysis but is also adding energy back into the system to allow for an entropy decrease which allows for the loop?
 
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You will require additional salt. We had steady rain for a couple of weeks early this swim season (or just before), and I lost quite a bit of salt from overflow. Had to add two 40 pound bags to get levels back up. I was most likely running a bit below where I want to be (3200) prior to rain, but it definitely contributed.
 
Had gone thru a lot of that; somewhere in there someone said, "When the chlorine that was created finishes purifying the water, it becomes salt and water once more." That's where my confusion lies. My understanding is that the "when the chlorine finishes purifying the water" it's combined chlorine. If it just goes back to salt and water (in the same amounts/concentrations), you're getting a free lunch.
 
Not a complete free lunch. You added electricity to the system to cause the electrolysis. The chemistry just completes its cycle back to salt.
 
texasmax said:
Had gone thru a lot of that; somewhere in there someone said, "When the chlorine that was created finishes purifying the water, it becomes salt and water once more." That's where my confusion lies. My understanding is that the "when the chlorine finishes purifying the water" it's combined chlorine. If it just goes back to salt and water (in the same amounts/concentrations), you're getting a free lunch.
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Combined chlorine is a temporary state while it is purifying the water. Assuming there is enough free chlorine available to finish sanitizing, combined chlorine is transitory.
 
texasmax said:
Had gone thru a lot of that; somewhere in there someone said, "When the chlorine that was created finishes purifying the water, it becomes salt and water once more." That's where my confusion lies. My understanding is that the "when the chlorine finishes purifying the water" it's combined chlorine. If it just goes back to salt and water (in the same amounts/concentrations), you're getting a free lunch.
Click to expand...
NaCl in water is Na+ Cl- What does that mean? the Sodium atom has donated an electron to the Chlorine atom when in water. In this state, neither are reactive.

In the salt cell, H+ and Cl- are electrically turned into Cl and H. The H will combine with another H and become Hydrogen Gas. The Cl is now FREE CHLORINE and very reactive. When it finds something to "kill", that will be oxidized, while the chlorine is reduced to Cl-. In the salt cell this is then cycled again.

So the salt cell actually causes a small water loss in the production of chlorine, not a loss of chlorine.

The "salt" loss is from "splash out" and rain. For me, it is rain. For every inch of rain, I lose about 1.6% of my water (assuming my pool is full). 5 inches of rain over a week, and my salt level will drop about 8% or about 240 ppm. One 40 lb bag of salt adds about 200 pm.
 
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