Swimming Pool Acid

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

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.

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

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