Minimum Pool Maintenance This Year! Why?

Chlorinating, maintaining the right chlorine levels,
chlorine problems. Dichlor, trichlor, cal hypo, bleach,
granules, chlorine pucks and chlorine sticks.
Allen G Myerson

Minimum Pool Maintenance This Year! Why?

Postby Allen G Myerson » Mon 20 Sep, 2010 01:04

The 90 % available chlorine is based on a chlorine gas equivalent. It is not the actual percent of chlorine in the tabs. Here is the equation:

2C3Cl3N3O3 + 6H2O <> 5H+ + 3OCl- + 3HOCl + 2C3H2N3O3

That's 425 ppm Cl2 for every 258 ppm of cyanuric acid. For every 10 ppm chlorine added by trichlor, the cyanuric acid will be raised by 6 ppm.

For example: Adding 1 pound of trichlor to 10,000 gallons of water will raise the Chlorine by 11, the cyanuric acid by 6.7 and lower the pH by 0.59.

Dichlor is acidic. Adding 1 pound of dichlor to 10,000 gallons of water will raise the Chlorine by 6.6, the cyanuric acid by 6 and lower the pH by 0.25.

Bleach is mostly pH neutral when accounting for consumption. There is some pH rise due to the sodium hydroxide, but it isn't very much.


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Minimum Pool Maintenance This Year! Why?

Postby floridapooltech » Mon 20 Sep, 2010 01:22

Allen G Myerson wrote:The 90 % available chlorine is based on a chlorine gas equivalent. It is not the actual percent of chlorine in the tabs. Here is the equation:

2C3Cl3N3O3 + 6H2O <> 5H+ + 3OCl- + 3HOCl + 2C3H2N3O3

That's 425 ppm Cl2 for every 258 ppm of cyanuric acid. For every 10 ppm chlorine added by trichlor, the cyanuric acid will be raised by 6 ppm.

For example: Adding 1 pound of trichlor to 10,000 gallons of water will raise the Chlorine by 11, the cyanuric acid by 6.7 and lower the pH by 0.59.

Dichlor is acidic. Adding 1 pound of dichlor to 10,000 gallons of water will raise the Chlorine by 6.6, the cyanuric acid by 6 and lower the pH by 0.25.

Bleach is mostly pH neutral when accounting for consumption. There is some pH rise due to the sodium hydroxide, but it isn't very much.


Your chemical composition is actually incorrect.

Depending on the inert ingredients by the manufacturer, (common) chemical reactions are as shown:

C3N3O3CL3
(Trichlor)

+ 3H2O
(water

--->

3HOCL
(Hypochloris Acid)

+ C3H3N3O3
(Cyanuric Acid)
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Allen G Myerson

Minimum Pool Maintenance This Year! Why?

Postby Allen G Myerson » Mon 20 Sep, 2010 01:33

At a pH of 7.5, about half of the hypochlorous acid will become hypochlorite and most of the cyanuric acid will be in the form of C3H2N3O3, which accounts for the 2.5H+ that I showed.
Allen G Myerson

Minimum Pool Maintenance This Year! Why?

Postby Allen G Myerson » Mon 20 Sep, 2010 01:46

232.41 grams of trichlor contains 212.718 grams of Cl2 equivalent, but only 106.359 actual grams of chlorine. The chlorine only makes up about 45.76 % of the trichlor. About 54 % of the trichlor is cyanuric acid.
Allen G Myerson

Minimum Pool Maintenance This Year! Why?

Postby Allen G Myerson » Mon 20 Sep, 2010 02:04

chem geek
As for using bicarbonate for not only raising the TA, but also raising the pH when using Trichlor, that is very inefficient as it would require a rather high TA level to keep the pH in balance by forcing more carbon dioxide outgassing.

I agree with you about the efficiency. However, my issue with using sodium carbonate is that it produces an unacceptable amount of cloudiness. It is also much more likely to combine with calcium and create a scaling or precipitation event. The locally high pH and carbonates can also cause other unwanted adverse reactions with metals etc.

Baking soda does not create any cloudiness and it raises the pH slowly and continuously. If you have the TA right, you can almost exactly offset the pH decrease caused by the tabs. This provides a much more stable pH instead of low pH followed by high.

Baking soda does not cost very much, and I think that the benefits far outweigh the slight cost advantage you would get by using the more efficient sodium carbonate.
Allen G Myerson

Minimum Pool Maintenance This Year! Why?

Postby Allen G Myerson » Mon 20 Sep, 2010 02:42

In fact, baking soda does cost less than sodium carbonate, so there would not be much cost savings anyway.

You can buy baking soda for about 60 cents per pound, whereas sodium carbonate will cost closer to $1.00 per pound.

Also, depending on the pH, there will be some pH rise directly as some of the baking soda takes up hydrogen ions to become carbon dioxide and water. At a starting pH of 7.0, about 18.3 % will become carbon dioxide and water.
Allen G Myerson

Minimum Pool Maintenance This Year! Why?

Postby Allen G Myerson » Mon 20 Sep, 2010 03:10

It takes roughly 1.6 times as much baking soda to neutralize the same amount of acid as 1 pound of sodium carbonate and sodium carbonate costs about 1.6 times as much as baking soda. Therefore, from a cost basis, you are at about break even.
mx357xm2

Minimum Pool Maintenance This Year! Why?

Postby mx357xm2 » Mon 20 Sep, 2010 04:22

swimnsaveusa wrote:Trichlor tabs contain 90% availabale chlorine, leaving only 10% for CYA and other additives. This being said, if the pool used the 2.4 ppm per day chlorine as you claim, then 10% of that would be 0.24 ppm CYA. leaving you with 160 days before a 40 ppm increase would have taken place, well within the spring/summer I claimed. Also, that does not account for the water loss/replacement which will lower the CYA levels even further!!! Also, that is if CYA took account for 100% of that 10% trichlor not taken up by chlorine.

Joey, please check the lids on the chemical containers in your store. Based on some of your posts, I am concerned that you might be being exposed to excessive levels of chlorine and other chemical fumes.
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Minimum Pool Maintenance This Year! Why?

Postby chem geek » Mon 20 Sep, 2010 09:26

Allen G Myerson wrote:2C3Cl3N3O3 + 6H2O <> 5H+ + 3OCl- + 3HOCl + 2C3H2N3O3

If you were trying to show half of the chlorine being hypochlorous acid and half being hypochlorite and most of the CYA being cyanurate ion, then the equation would be:

2C3Cl3N3O3 + 6H2O ---> 5H+ + 3OCl- + 3HOCl + 2C3H2N3O3-

where you left out a negative charge on the cyanurate ion. In practice, of course, most of the chlorine is attached to CYA as chlorinated isocyanurates since the water already has extra CYA in it -- that is, most of the HOCl and OCl- results in C3HClN3O3- and similar compounds (see this scientific paper for a full technical description of the equilibria involved).

As for the baking soda vs. pH Up, I only used Trichlor during my first year and a half of pool ownership around 7 years ago, but I used pH Up for pH control and though initial addition clouds the water, it cleared up soon after circulationg/mixing. Perhaps if the water is over-saturated with calcium carbonate (i.e. has a positive saturation index) that would be more of a problem, but when the water is balanced it shouldn't remain cloudy. The point about metal staining or precipitation from locally high pH is well taken.

As for pricing, if one is looking at the Alkalinity Up equivalent in stores of Arm & Hammer Baking Soda, then one needs to compare the pH Up equivalent which is Arm & Hammer Super Washing Soda (careful: not the laundry detergent).

As for the pH rising from baking soda addition, this is tricky to manage properly since the way you add the baking soda makes a difference as to how concentrated it gets locally causing bubbling that outgasses some carbon dioxide as you are adding it. I suppose with practice one can learn a technique that is consistent and keep a higher TA to keep things in balance, though that may be hard to achieve in places with hard water where a higher CH combined with that higher TA makes maintaining a decent saturation index more difficult (unless one maintains a lower pH, but one doesn't want to get too low). Also, for those who use pool covers, the outgassing of carbon dioxide will be limited so more direct sources of raising the pH would be needed (when using Trichlor, etc.). 20 Mule Team Borax is an option for raising pH that raises the TA about half as much bringing it close to where it started when the pH is restored. Of course, that eventually increases borate levels.
James Watson

Minimum Pool Maintenance This Year! Why?

Postby James Watson » Mon 20 Sep, 2010 10:04

chem geek,
What is your opinion about using sodium hydroxide to raise pH, if one can find it at a good price? Is there any reason, other than safety, that you know of why it isn't sold for use as a pH increaser?

It doesn't seem like it would be any more dangerous than many other pool chemicals such as muriatic acid.

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