Neutralizing ultimate acidty in dichlor and trichlor and more . . .

I did all calculations in my PoolEquations spreadsheet. In all cases, I added the chlorine in the "ADDED CHLORINE" section, clicked on the "Calculate pH/TA button" to calculate the chlorine increase, entered the amount from the blue box under "CHLORINE USAGE" for chlorine breakdown and put that into the yellow box next to it, clicked on the "Calculate pH/TA button" to find the resulting pH and TA from the addition and consumption/usage of chlorine. But then I have choices as I describe below.

Note that the answer in neutralizing the acidity depends on the amount of carbon dioxide outgassing that occurs. So I answered your questions in more than one way. I first answered in a way requiring carbon dioxide outgassing that along with the pH Up restores the pH and carbonate alkalinity to exactly where they were before, but that can result in a higher TA (since CYA counts towards TA). This was done using the "Calculate Acid/Base/Buffer" button after I adjusted TA to keep the carbonate alkalinity constant. I then answer your question using pH Up to restore pH assuming no carbon dioxide outgassing but resulting in an increase in carbonate alkalinity (from the pH Up which is sodium carbonate). This was done with the "Calculate Acid/Base/TA" button. This latter method is what you asked for, but in practice there is always some carbon dioxide outgassing so the former number gives you a bound for the amount of that needed to keep carbonate alkalinity constant.

Note that the starting pH is nearly irrelevant when using a strong base (e.g. lye) or acid (e.g. Muriatic Acid) for the neutralization computations, but for a weak base (e.g. pH Up or Borax) it makes some difference.

Quote:

Originally Posted by PoolDoc

Richard,

I wonder if you can calculate the following for me:

1. the lbs of borax decahydrate to neutralize the ultimate (not initial) acidity in 1lb of trichlor, in water holding a pH of 7.4
51.6 ounces weight of sodium tetraborate decahydrate with no carbon dioxide outgassing.

2. the lbs of soda ash to neutralize the ultimate (not initial) acidity in 1lb of trichlor, in water holding a pH of 7.4
13.8 ounces weight of soda ash with 0.36 pounds of carbon dioxide outgassing and increase in TA of 2.0 ppm (from the CYA)
26.0 ounces weight of soda ash with no carbon dioxide outgassing and resultant increase in carbonate alkalinity of 8.6 ppm and TA of 10.6 ppm

3. the lbs of borax decahydrate to neutralize the ultimate (not initial) acidity in 1lb of dichlor dihydrate in water holding a pH of 7.4
22.1 ounces weight of sodium tetraborate decahydrate with no carbon dioxide outgassing.

4. the lbs of soda ash to neutralize the ultimate (not initial) acidity in 1lb of dichlor dihydrate in water holding a pH of 7.4
5.9 ounces weight of soda ash with 0.15 pounds of carbon dioxide outgassing and increase in TA of 1.8 ppm (from the CYA)
11.1 ounces weight of soda ash with no carbon dioxide outgassing and resultant increase in carbonate alkalinity of 3.7 ppm and TA of 5.5 ppm

5. the effective CYA percentage of dichlor dihydrate (I have approximately 55% chlorine; 50% CYA)
Dichlor dihydrate molecular weight is 255.98 g/mole with the two chlorine atoms of 70.91 g/mole so that's 27.7% chlorine. The units of measurement of chlorine, however, are in ppm of chlorine gas equivalent BUT where only one chlorine is active since the other chlorine in chlorine gas becomes chloride when dissolved in water. This is why the % Available Chlorine which is the weight % of chlorine is double the 27.7% I just calculated so is 55.4% for pure Dichlor (in practice, it's 99% purity so is 54.8% Available Chlorine). As for the CYA, that is measured in CYA molecular weight which is 129.07 g/mole but there are no factors here so the CYA percentage is 50.4%. I think a far easier way to look at this is to just know that for every 10 ppm FC increase from Dichlor, it also increases CYA by 9.1 ppm since that is based on the fixed 129.07/(2*70.91) = 0.91 relationship that is independent of concentration of product (or whether it is dihydrate or not) or of pool size.

6. the effective CYA percentage of trichlor (I have approximately 90% chlorine; 55% CYA)
Trichlor molecular weight is 232.41 g/mole so the chlorine percentage is 2*3*35.443/232.41 = 91.5% while the CYA is 129.07/232.41 = 55.5%. Again, I think it's better to just know that for every 10 ppm FC increase from Trichlor, it also increases CYA by 6.1 ppm since that is based on the fixed 129.07/(3*70.91) = 0.607 relationship that is independent of concentration of product or of pool size.

Probably, I'm using incorrect terminology with respect to the acidity. What I'm look for are doses of borax and soda ash that, if added with the trichlor and dichlor, to a pool at pH 7.4 would cause the pool to RETURN to pH 7.4, after all available chlorine was consumed, and neglecting any loss of carbonate alkalinity.

I have other questions, as well:

7. when your spreadsheet (and presumably the Poolcalculator) calculates borates, are the ppm as boron or as borate, and if borate, which one?
Borates are measured as ppm Boron which has a molecular weight of 10.812 g/mole. This is why you can get a much larger weight requirement for chemical addition with either tetraborate or with boric acid and why the resulting TDS increase is higher since it's mostly boric acid in the water and that has a molecular weight of 61.83 g/mole.

8. do you know if all borate test methods are returning X ppm, where "X" is the same for all test methods?
They are supposed to as that is standard to measure ppm Boron, but I can't guarantee that. Ammonia tests sometimes return ppm-N and sometimes ppm-NH3 though those two are fairly close.

9. what is "X"; boron, borates, or something else?
X = boron