HCL vs H2SO4

[arff]

Dear All,
Still working my way to being fully out from under the influence of the pool shop.... I have read the old threads on which type of acid to use.

I am unable to find HCL instead of H2SO4 as all my local pool shops only seem to carry H2SO4 based "pH minus"; they all recommend Sulfuric acid, but to be fair to them, they admit that it is because that is what they have.

My recollection from my school years was that HCL is a stronger acid and has a pungent smell, which is why I assume people seem to prefer to work with H2SO4 when possible - marginally safer?

The forum advice to use HCL instead of H2SO4 is as usual very sound and I would like to go that way once my current batch of pH minus is finished (and I am close). Interestingly the last batch of pH minus the pool guy gave me to use with my auto-doser is 45% H2SO4 so pretty strong stuff... I think the laws have changed since and now and they are no longer able to sell more than 14.9% strength.

Since the pool shops do not seem to carry HCL based pH minus, do you have recommendations of what strength I should be using when I find it? So for example, Amazon seems to be selling 14.9% HCL from Bayrol which is ready to use, otherwise I can find industrial use HCL at 30% strength.

I know that chemically is does not matter and that it will likely be a case of accessibility, cost, and safety for handling; but aside from the usual care when dealing with strong acids and bases, are there any other recommendations / reasons for what I should run through my auto pH control system?

Thanks...

 

[mknauss]

Just like Dry Acid (sodium bisulfate), Sulfuric Acid ends up adding sulfates to your pool water. Sulfates build up in the water and destroy metals and plaster/concrete.

With a SWCG, you do not want sulfates in your water.

If that is all you can get, as long as you do large water exchanges to fresh often, either through rain, backwash, etc, you should be OK. But be ware SWCG manufacturers point out to NOT use Dry Acid (and by relationship Sulfuric Acid) in a pool with a SWCG.

If you can get HCl, then use it. Typically the higher strength is cheaper per unit volume. If you are adding it to tank for pH control, then dilute it with water. 2 or 3 parts water to 1 part acid.

 

[JoyfulNoise]

FYI - sulfuric acid is not safer than muriatic acid, in fact, it’s much, much more dangerous. Sulfuric acid at any concentrated strength, can cause serious and painful skin burns. By contrast, muriatic acid is much less reactive to human skin and you can easily get concentrated HCl on your hand without ever feeling it.

The odor threshold of HCl is much much lower than any concentration that can cause serious damage. Yes, the vapors have a very strong vinegar-mustard odor that will make you gasp, but that is fine as long as you are upwind of the bottle and in a fresh air open space. Smelling it does not make it dangerous and gives your body ample time to turn away and cough before any harm can possibly occur.

 

[arff]

Thanks - makes sense. I will go with the 30% HCL and dilute on a 1 to 2 basis with water.

Interestingly my SWCG manufacturer (Bayrol) recommends their own pH minus liquid which "has been specifically formulated for salt generators" and which is sulfuric acid based....

One question on the salt cell please: mine (and I assume all of them?) periodically reverses the polarity in order to clean and protect the cell. Their documentation states that increasing the frequency of this polarity reversal can significantly reduce the life of the cell. Can anyone explain why that would be?

 

[arff]

FYI - sulfuric acid is not safer than muriatic acid, in fact, it’s much, much more dangerous. Sulfuric acid at any concentrated strength, can cause serious and painful skin burns. By contrast, muriatic acid is much less reactive to human skin and you can easily get concentrated HCl on your hand without ever feeling it.

The odor threshold of HCl is much much lower than any concentration that can cause serious damage. Yes, the vapors have a very strong vinegar-mustard odor that will make you gasp, but that is fine as long as you are upwind of the bottle and in a fresh air open space. Smelling it does not make it dangerous and gives your body ample time to turn away and cough before any harm can possibly occur.

Yes you are correct - HCL is a 'stronger' acid meaning it is more dangerous to say metals..... but generally less so to humans - thank you for pointing that out. So I assume the main reason it is so much more prevalent is simply the manufacturing cost?

 

[JoyfulNoise]

Yes you are correct - HCL is a 'stronger' acid meaning it is more dangerous to say metals..... but generally less so to humans - thank you for pointing that out. So I assume the main reason it is so much more prevalent is simply the manufacturing cost?

Both HCl and H2SO4 are considered "strong" acids by chemical definition - they are fully miscible with water and they completely dissociate into a hydrogen ion (H+) and a conjugate base (either Cl- or HSO4-). They can both be dangerous to humans (or metal surfaces) but in the case of sulfuric acid, the conjugate base (HSO4-) has a very powerful desiccating effect that draws water out of the skin tissue, reacts with fatty tissue, and destroys cellular integrity. Chloride (Cl-), by contrast, does not have the same effect, mainly because the human skin layer is very effective at resisting chloride ion infiltration.

You are in Switzerland and the EU Zone. There may be regulations in effect that make HCl harder to buy and sell than H2SO4 (sulfuric acid is used a lot in farming and fertilizer production). So I don't really know why pool stores prefer one over the other but it could be due to manufacturing costs.

 

[arff]

Update, found an online source for reasonably priced HCL 30%.
Diluted it 2 parts water to 1 part HCL and replaced my H2SO4 pH Minus.
All's well so far.

Thanks for your feedback and recommendations!

I searched a fair amount and was unable to find ANY source of HCL for pH Minus specifically for pools near me.
From what I read, it is because the cost of H2SO4 is significantly lower.