Chlorine generation with less salt?

[aegerpa]

Why couldn't a manufacturer (or a tweaker) make a salt cell generate chlorine with lower levels of salt, like 1000 ppm? Wife doesn't like taste and feel of salt; I don't like adding bleach. Seems like 1000 ppm salt water would be conductive enough if the cell didn't have a default trip at 2500 ppm or so...I have 1000 ppm salt in now for eye comfort and it is great. Refreshing, can't taste it.

Thoughts and ideas?

 

[JohnT]

I'd expect it is because cell life would be shorter.

 

[jblizzle]

Have you been in a SWG pool? Most people can not detect the salt ... it is certainly much different than the ocean ... only 1/10 the level of salt.

 

[Suziqzer]

I would say the salt level is much lower than the ocean, however, myself and Hubby can both taste it. The first year we were a bit bothered by it, now I don't even notice it anymore... must have gotten used to it.

 

[samiguy]

Normal saline is 9000 ppm. Normal saline is used for eye wash, etc. The higher the salt, the higher the comfort level for eyes and membranes. Maybe a bit too much "thinking" than actual... Just my $ 0.02....

 

[jblizzle]

I can taste it. But whole family says it bothers the eyes less. Certainly nothing like the crusty feeling after being in the ocean.

 

[chem geek]

Why couldn't a manufacturer (or a tweaker) make a salt cell generate chlorine with lower levels of salt, like 1000 ppm?

It is technically difficult because there are two competing reactions at anode (chlorine generation plate). Chlorine or oxygen can be generated as shown below:

2Cl^- --> Cl₂(g) + 2e^- ..... E₀ = -1.358V
2H₂O --> O₂ + 4H⁺ + 4e^- ..... E₀ = -1.229V (at pH near 7 it's more like -0.8V)

From the above, you might think that oxygen gas would always be produced since it is thermodynamically favored, but there is a substantial overvoltage (analogous to activation energy) for producing oxygen gas from water (it varies by electrode material and is +0.56V for nickel, +0.77V for platinum, +0.91V for silver) so the chlorine reaction is favored if there is a sufficient level of chloride ions in the water. For today's saltwater chlorine generators, this minimum level is 3000 ppm for reasonably efficient production of chlorine. In residential spas where such efficiency is not needed because the volume of water is so small, 2000 ppm is a typical minimum salt level.

To be able to generate chlorine rather than oxygen at lower salt levels requires specialized plate materials and coatings and a small gap between the plates to overcome the higher electrical resistance (lower conductivity) of the water. The Ecoline™ FSRC Series works in freshwater with a TDS of 500-2000 ppm.