Ive been trying to work on this problem for a little now and I can seem to work it out.
Ill type it out exactly as it is written.
Your pool has 40,000 gallons and a combined chlorine reading of 2.3 ppm. How many pounds of calcium hypoclorite would be needed to reach breakpoint?
I know the answer is 11.5 pounds because the problems came with the answer sheet.
I need to know how to work it out.
If im leaving out any information needed Ill post it.
Please help.
Quick problem
Quick problem solved
Assuming breakpoint chlorination is 10x cc level we can calculate as follows:
I stand to be corrected if in error.
 40,000 gallons x 8.34 lbs = 333,600 lbs of pool water
 1,000,000 (parts cl in 1 lb) / 333,600 lbs pool water = 2.998 ppm cl in pool from 1 lb chlorine
 target chlorination is 10 x 2.3 ppm combined chlorine = 23 ppm chlorine
 required chlorine in lbs is 23 ppm / 2.998 ppm for 1 lb = 7.67 lbs chlorine
 cal hypo is typically 65% . So 7.67 lbs / 0.65 = 11.8 lbs cal hypo
I stand to be corrected if in error.

 Swimming Pool Pro
 Posts: 199
 Joined: Tue 08 Sep, 2009 10:40
 Location: Pleasanton, CA, USA
Quick problem
Or you can just use The Pool Calculator at poolcalculator.com.
For shock levels, you want to have about 40% of the CYA level. So if CYA is 30 ppm, shock level should be about 12 ppm.
You can read up on more of this at:
http://www.trouble freepool.com/poolschool/chlorine_cya_chart_shock
For shock levels, you want to have about 40% of the CYA level. So if CYA is 30 ppm, shock level should be about 12 ppm.
You can read up on more of this at:
http://www.trouble freepool.com/poolschool/chlorine_cya_chart_shock
Mark
Hydraulics 101 ; Pump and Pool Spreadsheets ; Pump Ed 101
18'x36' 20k gallon plaster/gunite pool, 1/2 HP 2sp pump, Aqualogic PS8 SWCG, 420 sqft Cartridge Filter, Solar Panels, 6 jet spa, 1 HP jet pump, 400k BTU NG Heater
Hydraulics 101 ; Pump and Pool Spreadsheets ; Pump Ed 101
18'x36' 20k gallon plaster/gunite pool, 1/2 HP 2sp pump, Aqualogic PS8 SWCG, 420 sqft Cartridge Filter, Solar Panels, 6 jet spa, 1 HP jet pump, 400k BTU NG Heater
Quick problem
I have two more problems needing help, and thank you for the last one it helped me alot to understanding the process.
An 80,000 gallon pool has a free active chlorine reading of 0.5 ppm and a Total available chlorine reading of 2.1 ppm. How much of the following is needed to reach breackpoint of each?
A. Gas Chorline (Pounds)
B. Sodium Hypochlorite (gallons)
C. Calcium Hypochlorite (pounds)
A pool has 200,000 gallons. The water test shows a Total Alkalinity of 30ppm, a PH of 7.0, a calcium hardness of 70 ppm, a water temperature of 94 degrees, and a TDS of 1,200 ppm.
a. What is the saturation Index?
b. Is the water Corrosive or scale?
c. What water balance factors need to be adjusted?
d. If the total alkalinity is to be adjusted to 100 ppm, how much sodium bicarbonate would you add?
An 80,000 gallon pool has a free active chlorine reading of 0.5 ppm and a Total available chlorine reading of 2.1 ppm. How much of the following is needed to reach breackpoint of each?
A. Gas Chorline (Pounds)
B. Sodium Hypochlorite (gallons)
C. Calcium Hypochlorite (pounds)
A pool has 200,000 gallons. The water test shows a Total Alkalinity of 30ppm, a PH of 7.0, a calcium hardness of 70 ppm, a water temperature of 94 degrees, and a TDS of 1,200 ppm.
a. What is the saturation Index?
b. Is the water Corrosive or scale?
c. What water balance factors need to be adjusted?
d. If the total alkalinity is to be adjusted to 100 ppm, how much sodium bicarbonate would you add?

 Swimming Pool Pro
 Posts: 199
 Joined: Tue 08 Sep, 2009 10:40
 Location: Pleasanton, CA, USA
Quick problem
The pool calculator will tell you everything you need to know: www.poolcalculator.com
Mark
Hydraulics 101 ; Pump and Pool Spreadsheets ; Pump Ed 101
18'x36' 20k gallon plaster/gunite pool, 1/2 HP 2sp pump, Aqualogic PS8 SWCG, 420 sqft Cartridge Filter, Solar Panels, 6 jet spa, 1 HP jet pump, 400k BTU NG Heater
Hydraulics 101 ; Pump and Pool Spreadsheets ; Pump Ed 101
18'x36' 20k gallon plaster/gunite pool, 1/2 HP 2sp pump, Aqualogic PS8 SWCG, 420 sqft Cartridge Filter, Solar Panels, 6 jet spa, 1 HP jet pump, 400k BTU NG Heater
Quick problem
rich wrote:I have two more problems needing help, and thank you for the last one it helped me alot to understanding the process.
An 80,000 gallon pool has a free active chlorine reading of 0.5 ppm and a Total available chlorine reading of 2.1 ppm. How much of the following is needed to reach breackpoint of each?
A. Gas Chorline (Pounds)
B. Sodium Hypochlorite (gallons)
C. Calcium Hypochlorite (pounds)
The rule that you need to add 10X the CC to achieve breakpoint is incorrect.
The rule came from the fact that it takes 1.5 moles of chlorine to oxidize 1 mole of ammonia (nitrogen). On a mass basis, chlorine is 70.9 grams per mole (measured as CL2) and ammonia is 14 grams per mole (measured as nitrogen). Therefore, it takes about 7.6 ppm chlorine per 1 ppm of nitrogen (1.5 x 70.9/14 =7.6). The 10X comes from using an excess to achieve a reasonable reaction rate.
However, chloramines are not measured as ppm nitrogen; they are measured as ppm chlorine. Therefore, the total chlorine only needs to be 1.5 times the CC, with an excess needed to achieve a reasonable reaction rate. Any chlorine added in excess of a total chlorine of 1.5 times the CC will be left after all of the nitrogen is oxidized. This can lead to situation where the residual chlorine is too high to swim after shocking is complete.
My recommendation is to raise the total chlorine to 5 times the CC level with a maximum residual of 10 ppm or 25 % of the cyanuric acid, whichever is higher.
For example, if the FC is 1.0 ppm and the CC is 3.0, then you would need a TC of 4.5 ppm to achieve breakpoint. If you added 10X the CC, you would raise the TC to 30 ppm and end up with 30  4.5 ppm = 25.5 ppm of chlorine. If you raised the TC to 14.5 by adding 10.5 ppm chlorine, then your residual FC should end up at 10 ppm.
The problem you are facing is that the people you are completing the test for probably want you to use the 10X the CC rule. Therefore, here is how to answer the question in a way they will consider to be correct.
2.1 ppm TC  0.5 ppm FC = 1.6 ppm CC. 10X 1.6 = 16 ppm
1 gallon of water weighs 8.35 pounds. The total weight of water is 80,000 x 8.35 = 668,000 pounds
Gas chlorine is the standard measure of chlorine so 1 pound of gas chlorine adds 1 pound of chlorine to the water (it is considered to be 100 % chlorine)
X/668,000 pounds = 16 pounds/ 1,000,000 pounds
X = 10.7 pounds of gas chlorine.
Assuming 12 % sodium hypochlorite, you would need 10.7/0.12 = 89 pounds of 12 % sodium hypochlorite. Sodium hypochlorite weighs about 9.2 pounds per gallon. Therefore, you would need 89/9.2 = 9.7 gallons of 12 % sodium hypochlorite.
Assuming 73 % calcium hypochlorite, you would need 10.7/0.73 = 14.7 pounds of 73 % calcium hypochlorite.
rich wrote:A pool has 200,000 gallons. The water test shows a Total Alkalinity of 30ppm, a PH of 7.0, a calcium hardness of 70 ppm, a water temperature of 94 degrees, and a TDS of 1,200 ppm.
a. What is the saturation Index?
b. Is the water Corrosive or scale?
c. What water balance factors need to be adjusted?
d. If the total alkalinity is to be adjusted to 100 ppm, how much sodium bicarbonate would you add?
pH = 7.0
pHs = (9.3 + A + B)  (C + D)
pHs = pH of saturation
A = (Log TDS 1)/10
B = 13.12 X log T + 34.55
T = temperature in Kelvin
C = log CH  0.4
D = log TA
A= 0.21
B= 1.9
C = 1.4
D = 1.5
pH s = (9.3 + 0.21 + 1.9)  (1.4 + 1.5) = 8.51
CSI = pH  pH s = 7.0  8.51 = 1.51
A negative CSI is corrosive.
The pH should be raised to at least 7.3, the TA should be raised to at least 50 ppm and the calcium level depends on the pool surface type. If it is plaster, then you want a CSI of at least 0.0
To increase the TA by 70 ppm, you need to add sodium bicarbonate. However, TA is measure in units of calcium carbonate.
X/1,670,000 pounds of water = 70/ 1,000,000
X = 117 pounds of calcium carbonate
Calcium carbonate is 100.1 grams per mole and sodium bicarbonate is 80 grams per mole. It takes 2 moles of sodium bicarbonate to equal 1 mole of calcium carbonate as far as TA is concerned.
117 pounds of calcium carbonate is 53,070 grams, which equals 530 moles of calcium carbonate or 1060 moles of sodium bicarbonate, which equals 84,827 grams or 187 pounds
Quick problem
Note: When calculating the CSI, it's important to measure the cyanuric acid, as that has an effect on the TA.
You need to subtract about 1/3 of the Cyanuric acid from the TA to get the Carbonate Alkalinity. In your problem, I assumed a cyanuric acid of 0 ppm since it was not given. However, you should never assume such things; they must be measured.
D = log Carbonate Alkalinity.
In the first problem, the amount of chlorine to be added should achieve a TC of 10 X the CC. Therefore, the amount of chlorine to add would be 16 ppm  2.1 (existing TC) = 13.9 ppm.
You need to subtract about 1/3 of the Cyanuric acid from the TA to get the Carbonate Alkalinity. In your problem, I assumed a cyanuric acid of 0 ppm since it was not given. However, you should never assume such things; they must be measured.
D = log Carbonate Alkalinity.
In the first problem, the amount of chlorine to be added should achieve a TC of 10 X the CC. Therefore, the amount of chlorine to add would be 16 ppm  2.1 (existing TC) = 13.9 ppm.

 Pool Industry Leader
 Posts: 2382
 Joined: Thu 21 Jun, 2007 21:27
 Location: San Rafael, California
Quick problem
Allen G Myerson wrote:However, chloramines are not measured as ppm nitrogen; they are measured as ppm chlorine. Therefore, the total chlorine only needs to be 1.5 times the CC, with an excess needed to achieve a reasonable reaction rate. Any chlorine added in excess of a total chlorine of 1.5 times the CC will be left after all of the nitrogen is oxidized. This can lead to situation where the residual chlorine is too high to swim after shocking is complete.
Almost, but not quite. You are forgetting that 1 of the 1.5 chlorine relative to CC is already part of CC, if it is monochloramine (that is, one mole of chlorine has already combined with one mole of ammonia to form monochloramine). It actually only takes 0.5x chlorine to oxidize monochloramine in terms of stoichiometry, though to get "over the hump" it might take 1x. Then there is urea where monochlorourea may often be the dominant component of CC. In that case, it takes 2x chlorine to oxidize monochlorourea with 3x possibly needed to get "over the hump". In any event, your rule of 5x and adjustments relative to CYA level are fine since in practice so long as there is ANY FC measurable, then oxidation of CC is occurring. A higher FC just makes it go faster.
Quick problem
chem geek wrote:Almost, but not quite. You are forgetting that 1 of the 1.5 chlorine relative to CC is already part of CC, if it is monochloramine (that is, one mole of chlorine has already combined with one mole of ammonia to form monochloramine). It actually only takes 0.5x chlorine to oxidize monochloramine in terms of stoichiometry, though to get "over the hump" it might take 1x.
Note that I said that the total chlorine needs to be 1.5 times the CC, which takes into account both the FC and the CC.
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