Salt water generators are closed systems... what?

[ajw22]

. But if you use dichlor or trichlor pucks, those don't contain any sodium.

Yes it does. In 10,000 gallons 8 oz of Trichlor contains 4.5 ppm of salt. 8 oz of dichlor contains 2.7 ppm of salt. You will find the salt it contains proportional to the FC it contains.

Because if not, if you run your pool on things like tabs and cal-hypo for a long time and never introduce any sodium

Tabs do introduce sodium to the pool.

 

[Abnaxis]

You know, I just found this thread after asking a very similar question about Cl- build-up. Everything makes sense but I'm hung up on something:



To be pedantic, I'm not sure this is correct. I'm pretty sure the water does that. Only the Cl- participates in the reaction in the salt sell; the Na+ is needed to make the water conductive. You don't actually need the sodium to make hypochlorous acid but the electrolysis would be impossible without it. In theory, you could use other chloride salts to get the same effect. I hope someone will correct me if I'm wrong about this.



Ok here we go, continuing the thought from above. When you say "salt" here (and when we test salt levels in the pool) most people probably think "table salt" like @JJ_Tex said, but I assume we're using the chemistry definition and if my understanding is correct, the sodium doesn't really matter. If you use bleach or chlorinating liquid, that's NaClO (sodium hypochlorite) and it will provide enough Na+ to make this work like you describe. But if you use dichlor or trichlor pucks, those don't contain any sodium. Is there some other positively-charged ion the Cl- will bond with in this case?

Because if not, if you run your pool on things like tabs and cal-hypo for a long time and never introduce any sodium, then you decide to convert to salt... is the excessive amount of existing Cl- going to cause a problem?

I know we don't like those products here (for good reason) but I come across so many people who swear by them. And these days with the national shortage and everyone converting to salt, I'm thinking this could be a very plausible scenario.

I'm not with my test kit to double check, but I'm like 80% certain any salinity test is (effectively, oversimplification) testing for available Cl- ions regardless of what ionic compounds it comes from. So it doesn't matter if the chlorine is from dichlor-- either way you should test salinity before you add salt for a SWG, and the salinity test doesn't distinguish between Cl- that comes from dichlor or NaCl

The way I've always thought of it, and I might be completely off in my mental model, is that Na+ necessary for Cl- to be present at all, but the presence of Cl- is what's really important. Ions in water only result from the breakdown of an ionic compound, which doesn't happen without a positive and negative ion going into the solution.

EDIT: also apparently tabs have salt in them and I shouldn't have taken you at your word that they don't without waiting for someone else to reply

 

[JamesW]

Dichlor has sodium.

Trichlor does not have sodium, but it does have chlorine, which becomes chloride. So, it is counted as salt.

Salt breaks into sodium and chloride as soon as it dissolves in the water.

The cell only needs chloride and the sodium is completely irrelevant to the SWG.

The K-1766 only measures chloride.

 

[JamesW]

Calcium hypochlorite does not contain sodium, but calcium chloride is a salt.

 

[JamesW]

If you chlorinate with chlorine gas, you only add chloride and the level would eventually be high enough to convert to a SWG with no sodium added or needed.

However, chlorine gas or trichlor are acidic and you end up adding sodium as you raise the pH.

Sodium hydroxide, sodium carbonate, sodium bicarbonate, sodium tetraborate etc all contain sodium.

So, in most cases, the amount of sodium is close to the amount of chloride.

You could add chloride from calcium chloride, magnesium chloride, lithium chloride etc and the SWG would work just as well, but it would probably scale up more than with sodium.

 

[riny]

In 10,000 gallons 8 oz of Trichlor contains 4.5 ppm of salt. 8 oz of dichlor contains 2.7 ppm of salt.

Ok let's be precise here. Do you mean SALT as in any anion/cation compound, or specifically NaCl? According to wikipedia anyway:

Dichlor = C₃HCl₂N₃O₃
Trichlor = C₃Cl₃N₃O₃

There's no sodium in either of these. I understand that they'll both leave you with plenty of Cl- at the end of the chain, but I was trying to figure out how that translates to "salt" unless you're also introducing Na+ or some other cation.

chlorine gas or trichlor are acidic and you end up adding sodium as you raise the pH

Yes, now this makes sense!

 

[JamesW]

Dichlor = C₃HCl₂N₃O₃

There's no sodium in either of these.

Dichlor is Sodium dichloro-s-triazinetrione dihydrate

Sodium dichloroisocyanurate

NaC₃Cl₂N₃O₃ •2H₂O

CAS no. 51580-86-0

So, dichlor does contain sodium.

 

[JamesW]

 

[JamesW]

There is an anhydrous and a dihydrate version.

 

[riny]

Ah, very interesting. I guess sodium is just inescapable.

 

[JoyfulNoise]

Isocyanurates are manufactured compounds and are acidic during the production process. Typically the last step in the process is to neutralize the acidic organic compound with a strong base like sodium hydroxide. That then creates the sodium “salt” of the cyanurate anion. Sodium adducts on organic acids like cyanurates typically make them more soluble in water and easier to handle.

The term “salt” in chemistry is not very specific. But it is used in the context of SWGs because sodium chloride, aka “table salt”, is used to provide the chloride anion to the solution. Testing is standardized against the molecular weight of sodium chloride so the units of the K-1766 are described as “part per million of sodium chloride” even though the actual chemical reactions of the test are specific to the chloride ion. SWGs also assume their units to be read in as molar mass of sodium chloride even though it’s the chloride ion that only matters.