High pH, SWCG, No Access to Muriatic Acid

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V

vvbrock

0
Sep 29, 2014
10
Pucallpa, Peru
Hello All,
Just wanting to find out what your advice is. I am continually trying to lower my pH. I bought an HTH product called pH minus but in less than a week, i've used more the whole jug (7lb). I am thinking of buying a 50lb bag of sodium metabisulfite as this HTH is over 20 dollars per bottle here in this jungle town, but have read that maybe this is not a good idea? I have no access to Muriatic Acid as I live in a "Red Zone" for cocaine production. Also, is dry acid going to mess up my salt water chlorine generator as it contains sulfur? I don't know what other option I have.
 
Good Day, one thing that you have not talked about is your alkalinity level. High alkalinity will cause the pH to stay high. I would use only the dry acid (sodium bisulfate) to adjust the pH if Muratic acid is not available. Follow the directions to get your alkalinity down if it is high.

John the Hayward tech.
 
Thanks for your response. I finally got my test done today. The TA is at 150, and my CH is at 60. Both are way out of whack. According to the pool math site, I need about 15lb of dry acid. and about 110lb of Calcium Chloride. I am trying to see what police permission I need to get for ordering in some muriatic acid, but it probably won't happen. As I have only just started this pool, I have not yet turned on the SWG. I plan on that in a few weeks. Do I need to fool with Boric acid as well?
 
Dry acid won't be a problem for some time. However if you keep using it in large quantities like that for a long time, the sulfate level will eventually get high enough to cause problems for the SWG cell plates.
 
See how to Lower Total Alkalnity. You can lower that to 70 ppm and that should help a lot. Your CH should be increased if you have a plaster pool surface -- if it's vinyl and you have no exposed grout in tile, then you don't need calcium in the water.

If you had access to boric acid [EDIT] (Borax would require acid so probably not a good choice -- boric acid would be better) [END-EDIT], then you could use 50 ppm borates in your pool for additional pH stability after you get your TA lower. However, for your size pool that can get pretty expensive.
 
If your pool does not have plaster or grout, then you probably don't need calcium. Calcium would only increase your risk of scaling the cell.

Sodium metabisulfite is a reducing agent (chlorine neutralizer), and would not be suitable for lowering pH.

Muriatic acid would be the best choice for controlling pH rise. Second choice would be sulfuric acid. However, I would think that if you couldn't get one, you couldn't get the other.

Carbon dioxide would work, but it would probably be very expensive.

Alternating using the SWG with trichlor tabs would help. The tabs are net acidic, and would lower the pH and TA. You could use them when the pH needed to be lowered and the cyanuric acid level was below 80 ppm. You would need to ensure that there would not be a conflict with the two systems. For example, you would need to make sure that concentrated trichlor did not get in the cell, and you would need to make sure that the chlorine and hydrogen gasses produced by the cell did not get into a tab feeder.

Alternating using the SWG with chlorine gas would help. However, that would have multiple issues including availability, cost and safety.

Maintaining the pH at the high end of the range (about 7.8) would help. In that case, a pH meter would be helpful to give you more precise control over the pH.
 
I do have a plaster pool. Actually we have the stonescapes mini pebble. Not a great DIYer project to try to tackle, but when you have no other option.... So just using trichlor tabs will bring my pH down? Should I not be using liquid chlorine? I have been using 7.5% liquid chlorine. Could this be causing some of my problems? I suppose the first thing to do is to try to get my wildly off numbers right and then focus on the maintenance.... So 15lbs of dry acid and 110lbs od calcium... I should be able to get that here in a couple of weeks. In the mean time I will be using trichlor tabs to regulate chlorine. Hou said keep pH on the high end of the range? Won't that burn your eyes? Thanks for your help guys.
 
I would avoid adding dry acid as much as possible. Tabs will provide chlorine and cyanuric acid. Tabs will also lower the pH and TA. I would suggest alternating between tabs and liquid depending on the pH and CYA level. For high pH and low CYA, use tabs. For good to low pH and OK CYA, use liquid.

After 30 days, you can add the salt and begin to use the SWG. The SWG should be mostly pH neutral. I would suggest switching to tabs to help control the PH whenever the pH is high and the CYA is less than 80.
 
Hi! I remember your first post describing the pool:
http://www.troublefreepool.com/threads/85808-New-pool-in-Jungles-of-Peru

How did you make out in finding a decent test kit? I seem to remember that you ordered one, but it got stuck in customs...

Regarding your trichlor question, yes, the cyanuric acid in trichlor will lower pH (see PoolMath for numbers). But, as you probably realize from reading on the forum, you don't want to keep adding CYA to your pool indefinitely. Do you know how much CYA you currently have (either by test result, or from your knowledge of what you have put into the new pool)?
 
Note: It's the chlorine in trichlor that makes tabs acidic. The cyanuric acid is actually in the form of cyanurate, which is a base and partially offsets the acidity of the chlorine.
 

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JamesW said:
Muriatic acid would be the best choice for controlling pH rise. Second choice would be sulfuric acid. However, I would think that if you couldn't get one, you couldn't get the other. Carbon dioxide would work, but it would probably be very expensive.
Click to expand...

Hello, I have a similar problem with PH constantly trying to rise ... your quote gave me an idea, maybe a stupid one ... if CO2 would reduce PH, why couldn't we just dump a bunch of dry ice into our pools? Or, would it take an astronomical amount of dry ice and/or $$$ to do this?
 
Some commercial/public pools do in fact use injected carbon dioxide for lowering the pH, but they use gas compressed in containers as liquid carbon dioxide, not dry ice. Of course, it's best to lower the TA to minimize the CO2 outgassing in the first place.
 
I've seen a co2 injection system for sale on some websites. It basically is a ph probe and a solenoid that attaches to a co2 cylinder. I don't know how much the co2 affects the ph of the pool, but it costs about $10 to fill a 5lb cylinder around here. That's a gallon and a half of muriatic acid.


Sent from my iPhone using Tapatalk
 
The addition of carbon dioxide to the pool is equivalent to adding acid plus baking soda where it lowers the pH with no change in TA. The technical equivalency is shown below:

-TA ..... +TA
HCl + NaHCO3 = CO2 + H2O + NaCl
Hydrochloric Acid + Sodium Bicarbonate = Carbon Dioxide + Water + Salt

One gallon of full-strength Muriatic Acid (31.45% Hydrochloric Acid) plus 7.015 pounds of sodium bicarbonate are equivalent to 3.676 pounds of carbon dioxide. So 1-1/2 gallons of acid is equivalent to 5.5 pounds of carbon dioxide. The acid is usually at least $5 per gallon so 1-1/2 gallons is at least $7.50 and you also need to add bicarbonate. So the overall pricing is roughly comparable for what you are getting, but in commercial/public pool quantities the carbon dioxide approach is usually far less expensive since acid is around $2.90 per gallon, bicarbonate at $0.34 per pound and carbon dioxide at $0.25 per pound.

However, to properly add carbon dioxide to a pool requires a booster pump with a properly sized efficient gas transfer Venturi injector into a slip-stream joining the main return stream. Though you can add the gas in more simplistic ways, you risk having the gas not fully dissolve and just outgassing out of the pool far too soon.
 
Chem geek- I appreciate every post of yours I read. Being fairly educated, and in the chemical industry, I half way keep up with most of your posts. Just out of curiosity, what field do you work in?


Sent from my iPhone using Tapatalk
 
Note that the primary reason that I mentioned carbon dioxide is that the poster does not have access to muriatic acid. In my opinion, carbon dioxide is usually not the best choice for pH control.
 
Gotcha. I've just seen it as an option. Albeit, not the best option for me.

I know that carbon dioxide makes carbonic acid in solution. I just wasn't sure how strong it was in relation to muriatic acid. From my experience with HCL at work, and stripping co2 from product, I assumed it was way weaker.


Sent from my iPhone using Tapatalk
 
n240sxguy said:
Chem geek- I appreciate every post of yours I read. Being fairly educated, and in the chemical industry, I half way keep up with most of your posts. Just out of curiosity, what field do you work in?
Click to expand...

I don't work in the pool/spa industry and I'm not a chemist. I did major in chemistry and physics (field major -- they didn't allow a double major due to too many overlapping course requirements) but for work I've done primarily computer software design and programming along with color and imaging algorithms.

n240sxguy said:
I know that carbon dioxide makes carbonic acid in solution. I just wasn't sure how strong it was in relation to muriatic acid. From my experience with HCL at work, and stripping co2 from product, I assumed it was way weaker.
Click to expand...

The weakness of carbon dioxide as an acid is not that relevant since the purpose is not to get the pH very low but simply to lower the pH some relatively small amount. The pKa of carbonic acid is around 6.3 so moving the pH say from 7.8 to 7.5 in 10,000 gallons with typical pool TA, CYA, etc. requires 8.15 fluid ounces of full strength Muriatic Acid and that is (241 ml) * (1.159 g/ml) * (31.45%) / (36.46094 g/mole) = 2.41 moles. The amount of carbon dioxide for the same pH change under the same conditions would be 0.246 pounds and that is (112 g) / (44.01 g/mole) = 2.55 moles. So on a molar basis the carbon dioxide is nearly as strong as hydrochloric acid for the example given. Of course, with the Muriatic Acid the TA drops by 3.2 ppm while with CO2 there is no change in TA.

Now if I were to try and go from 7.5 to 7.2, then with Muriatic Acid I get 13.13 fluid ounces so (389 ml) * (1.159 g/ml) * (31.45%) / (36.46094 g/mole) = 3.88 moles while the amount of carbon dioxide needed is 0.420 pounds and that is (191 g) / (44.01 g/mole) = 4.33 moles so you can see that carbon dioxide is less efficient than Muriatic Acid when the pH is lower which makes sense as the pH is approaching the pKa. Nevertheless, even in this case it's a difference of around 12%.
 

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