Swimming Pool Acid

[liz+3]

Hello all,

I just purchased some Kem-Tek swimming pool acid for lowering pH. The label indicates it is 38.5% sulfuric acid. I didn't realize the label did not say muriatic acid when I bought it. I purchased the acid at a discount store - 6 gallons for $9.00 - closeout price - bought the last 6 gallons!

I have been using muriatic acid (HCL) for lowering my pH. Can I use this Kem-Tek product even though it is sulfuric and not HCL acid or did I just waste $9?

Thanks.

Liz

15000 gallon IG Gunite with Diamond Brite (3.5 - 5 - 3.5)
7 Ft. Diameter Raised Spa with Spillway
Intellichlor IC20 SWCG
Intelliflo 4X160 Pump
60 Sq. Ft. DE Filter
Spa Heater
Jet-Vac

[chem geek]

You can use it. The only downside is that you will add to the sulfates in your water. You also end up adding sulfates when you use non-chlorine shock (potassium monopersulfate or KPMS). This is not a problem unless the sulfates get really high at which point it starts to affect water chemistry a little bit (makes the water more corrosive and less likely to scale), but it would take a heck of a lot of sulfates to cause that so I wouldn't worry about it (300 ppm of sulfates would be equivalent to lowering the pH by 0.1). Just get Muriatic Acid whenever you run out of this stuff.

As for how much to use, it is very close to the Muriatic Acid in effective acid concentration per volume, though you can verify this by looking at the bottle to see how much it says to use to lower pH. Though sulfuric acid has two hydrogen (H2SO4) compared to hydrochloric acid (HCl), it is more than double the molecular weight so this along with the 38.5% vs. 31.45% cancels out (I suspect they chose 38.5% concentration so that the acid was close to the 31.45% Muriatic Acid concentration).

One cup of sulfuric acid in 10,000 gallons adds 5.9 ppm of sulfates so it would take a whole lot of acid before you started to see any impact from the sulfates. One cup of non-chlorine shock (KMPS) adds 5.1 ppm of sulfates so is about the same in that effect.

Richard

[liz+3]

Thanks Richard.

Glad I didn't pass up a great deal.

Liz

15000 gallon IG Gunite with Diamond Brite (3.5 - 5 - 3.5)
7 Ft. Diameter Raised Spa with Spillway
Intellichlor IC20 SWCG
Intelliflo 4X160 Pump
60 Sq. Ft. DE Filter
Spa Heater
Jet-Vac

[CarlD]

It's not that great a deal--ultimately continued use can give you problems that hydrochloric acid won't.

What Chem_Geek is basically saying is it's OK to use it, since you have it, but you have to watch for things building up, unlike Muriatic Acid.

I would not buy it again, though.

[waterbear]

It has about the same side effects as using dry acid (sodium bisulfate) without the convienence factor. With a SWG, hydrochloric acid (muriatic acid) is my first choice.
Edit: Muriatic acid adds chloride ions to the water so the salt (sodium chloride) that the SWG uses is 'reformed' after generating chlorine. Sufuric acid and dry acid do not do this. (Richard, I know this is very oversimplifed and not totally accurate but it is close enough to the correct annswer without getting too technical:D). As Carl said, it's ok to use but when it's gone you would be better off with muriatic acid in my opinion.

[liz+3]

All right, you all said it is OK to use but I should watch out for things building up in the pool (ie: sulfates). So, if I use these 6 gallons of sulfuric acid over the next couple of months, how much "stuff" will build up in my pool and should I be concerned about this buildup? Is there any way to test for the sulfates?

Based on the respones, I am highly considering not using the sulfuric at all - that way I won't have to worry about sulfates.

I also will never again buy anything but HCl for my pool!!

Thanks,

Liz


15000 gallon IG Gunite with Diamond Brite (3.5 - 5 - 3.5)
7 Ft. Diameter Raised Spa with Spillway
Intellichlor IC20 SWCG
Intelliflo 4X160 Pump
60 Sq. Ft. DE Filter
Spa Heater
Jet-Vac

[chem geek]

Each gallon of 38.5% sulfuric acid will add [EDIT] 15.7 [END-EDIT] ppm of sulfates so 6 gallons will add [EDIT] 94.3 [END-EDIT] ppm of sulfates which [EDIT] not have much affect on [END-EDIT] your water chemistry. You could compensate for this (though you really don't have to since the effect is so small) by running your pool with higher TA, CH or pH, but again I don't think this is a big deal.

We're not trying to scare you. Personally, I think you can use your 6 gallons in one season and be OK with it, but don't use it again. Eventually through splash-out, backwash (if you have a filter that needs it), and dilution from winter rains (if you live in a climate that doesn't freeze so that you let winter rains overflow your pool) will eventually reduce the amount of sulfates in the water.

I do not know of a test on the market for sulfates. Taylor does not appear to have one. That doesn't mean there isn't one out there, but I just don't know about it (maybe someone else does). I don't think it's a problem if you don't use any more sulfuric acid after this batch.

Richard

[waterbear]

6 gallons of sulfuric acid in 15000 gal pool water over a period of time is not going to increase your sulfates that much. Like I said before, it's about the same as using pH increaser (dry acid), which many people use on a regular basis. Also using non chlorine shock (MPS) adds a lot of sulfates to the water and a lot of people use that on a regular basis (weekly if they are doing it correctly). There is some evidence (depending on who you talk to) that HIGH levels of sulfates in pool water can cause damage to plaster surfaces over time (along with several other causes) but you will not be anywhere near a high level from the amount that you have. Just use it up and when it's gone switch over to muriatic acid (and don't lose any sleep over it!:D). I would not use it for cleaning your salt cell, however. For that muriatic acid is used.

[liz+3]

OK, I feel a lot better now.

Thanks for the help everyone.

Liz.

15000 gallon IG Gunite with Diamond Brite (3.5 - 5 - 3.5)
7 Ft. Diameter Raised Spa with Spillway
Intellichlor IC20 SWCG
Intelliflo 4X160 Pump
60 Sq. Ft. DE Filter
Spa Heater
Jet-Vac

[CarlD]

Glad you feel better. I didn't want you to feel you wasted your money and couldn't use the sulfuric acid. But, on the other hand, I didn't want you buying more of it--stick to muriatic acid or dry acid. (Dry Acid is much safer and easier to use which is why I like it)

[chem geek]

Carl,

Is there a dry acid other than Sodium Bisulfate? The only one I've seen is 93.2% Sodium Bisulfate which actually adds about twice as much sulfate to the water for the same acid effect as sulfuric acid. 1 cup of 31.45% Muriatic acid is about equivalent in acid strength as 1 cup of 38.5% Sulfuric acid and is about equivalent in acid strength as 10.7 ounces of 93.2% Sodium Bisulfate dry acid. However, whereas 1 cup of Muriatic acid doesn't add any sulfate (it adds 1.2 ppm of chloride ion), 1 cup of Sulfuric acid adds 1.0 ppm of sulfate while 10.7 ounces of Sodium Bisulfate dry acid adds 2.1 ppm of sulfate (and 0.4 ppm sodium ion).

I incorrectly calculated the amount of sulfates from Sulfuric acid but corrected my earlier post (I only added sulfuric acid to my spreadsheet when I saw this thread and made a mistake in the sulfates calculation). There's hardly any problem at all with the 6 gallons of sulfuric acid though I agree switching to Muriatic acid is wise. As for Sodium Bisulfate, as I indicated above it adds twice as much sulfate for the same acid effect and I know there's no mistake in that (sulfuric acid is H2SO4 providing two hydrogen for each sulfate while sodium bisulfate is NaHSO4 providing one hydrogen for each sulfate).

Richard

[CarlD]

No, that's the only one.

I may be getting in over my head here--I rarely use acid of any sort. Of course, I rarely use Borax either--I don't adjust pH if it's between 7.3 and 7.8.

I have to take your word that Dry Acid adds more sulfates than Sulfuric acid...But dry acid is a trade-off with Muriatic in that it's safer and easier to use.

Since I use it so rarely it's not an issue for me.

[chem geek]

I totally agree. Even adding one pound of dry acid each week per 10,000 gallons (which is equivalent to about 1.5 cups of liquid Muriatic or Sulfuric acid) would add about 250 ppm over 6 months which only starts to affect water chemistry (it's equivalent to a drop in pH of 0.1 as far as calcium carbonate equilibrium is concerned).

Adding one pound of non-chlorine shock (potassium monopersulfate or KMPS) each week per 10,000 gallons would add about 200 ppm sulfate over 6 months.

So if someone had a regimen of adding these chemicals on a regular basis and did this over years without significant dilution or replacement of their water, then I could see a problem slowly emerge, but as waterbear points out the problem is not worth worrying about until the sulfates get really high.

Personally, I use winter rains to dilute my pool by about half each season just to keep whatever is building up under control, but that costs me in chemicals each season as I have to build back up the calcium, carbonate and CYA. If I start using salt (1000 ppm) and borates (50 ppm Boron) next year, then I'd have to add those as well. Perhaps I'll stop my annual dilution regimen!

Richard

[PatL34]

If you are using a SWCG, then IMHO, the only acid you should be using is muriatic acid. It makes things easier.
Pat