Calculating PPM by hand

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C

cdoc83

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Jul 7, 2016
7
Preston, Idaho
Hey everyone! I know this site has a great calculator to determine how much chlorine to add to achieve a desired PPM, but I'd like to be able to calculate the same result by hand. According to Wiki (https://en.wikipedia.org/wiki/Parts-per_notation), .0001% = 1 PPM. Therefore, if I have 1,000 gallons (128,000 ounces) and add 1 TBSP (.5 ounce) of pure chlorine (as in 100% bleach, which I know doesn't exist publicly, just using it for easy calculations for now), I get 3.9 PPM (.5 divided by 128,000.5 = .0000039). If I input the same values, the calculator agrees perfectly.

However, if we up the values significantly, the calculator no longer agrees. For example: With 50,000 gallons, to get to 4 PPM the calculator determines 25 ounces of pure chlorine. However, hand calculating is as follows: 50,000 gallons = 6,400,000 ounces. Add the 25 ounces for 6,400,025 total ounces. 25 divided by 6,400,025 = .0000039, or 3.9 PPM, not 4 PPM. Just to make sure the calculation simply doesn't include the added 25 ounces, 25 divided by 6,400,000 also equals 3.9 PPM. At first I thought maybe the calculator just rounded, but changing the desired level in the calculator to 3.9 changes the required ounces to 24. So, it's apparent I'm missing something here...

Also, if that question can be answered, I haven't worked the math on substituting pure chlorine for the regularly available 5%, 6%, or 8.25% if anyone has a formula for that.

As a final FYI, the only reason I'm trying to figure this out is to preserve the formula for occasions where technology is not readily available, such as natural disasters or winter storms. I know the page can be downloaded to the local computer, but if the power is out, it doesn't do much good.

Thanks!
Cam
 
Cam - First question I have. If I go to pool Math page and enter 50k gallon pool, FC "now" of 0, and "Target" FC of 4.0 using 100% bleach, I get 60 ozs of bleach. Where are you getting 25 ozs?

Once that is answered, then I am curious about the rounding aspect. But I will elaborate once we agree upon the amount of "100% bleach" to add to a 50k gallon pool.
 
That is curious, here's a screen shot for proof of what I'm seeing:


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Well, it seems like someone has ripped off the calculator found on this site at poolcalculator.com, which is where the 25 ounces were coming from. Re-doing the math with the 60 ounces now...
 

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Sweet, thanks! Ok, using the calculator actually found on this site, it seems the math is worse... 50,000 gallons = 6,400,000 ounces, plus the 60 ounces of chlorine = 6,400,060 ounces. 60 ounces chlorine divided by 6,400,060 total ounces = .00000937, or 9.4 PPM. Now I'm more confused...
 
No problem. Glad I caught that. But that is even more obscure now. The old vs new calculator is disagreeing by 150%. At least the old calculator was close to your hand calculation. (24 vs 25 ozs). But the new POOL MATH calculator is now a 1.5 times multiple of doing a hand calculation!!!! (24 vs 60 ozs).. You agree with that assessment right?
 
Cam - Here's an interesting theory. Strictly theory. I'll lay it out there and perhaps you may see some credence in it:

Being that there is no such thing as 100% bleach in real life, perhaps it is an unsolvable equation. But look at my snap shot above of the current POOL MATH calculator. There's an option in the drop down for "Chlorine Gas", which in theory should be 100% pure. (After all Chlorine is a gas as depicted in its placement on the Periodic Table of Elements.) But I digress....

Back to the drop down in the menu. Notice that if you choose "chlorine gas" from the drop down, you do get 27ozs as your answer. At least this is closer to your 24 oz hand calculation.

I know that's not an answer to this conundrum, but perhaps it can steer you in the right direction.
 
cdoc83 said:
................... As a final FYI, the only reason I'm trying to figure this out is to preserve the formula for occasions where technology is not readily available, such as natural disasters or winter storms. I know the page can be downloaded to the local computer, but if the power is out, it doesn't do much good.

Thanks!
Cam
Click to expand...
Welcome to the forum!

While I'm a math & science nut, it's much easier to just use the "effects of adding chemicals" section of Pool Math.

Once you enter your pool's volume up top, scroll down to the above mentioned section, pick a source of chlorine, and play with the amount until you get 1ppm.

For instance, that works out for my pool at 7oz of 12.5%, 8.5oz of 10%, or 10oz of 8.25%. If I want to raise my FC 3ppm & I'm using 12.5% I just measure out 21oz of chlorine and add it to the pool, if it is still standing during said natural disaster, or not frozen over during said winter storm LOL.

Easy Peasy.

(I'd still be interested in any formulas though...)

Dom
 

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Mike has hit on part of the issue. Try putting in 10% bleach and you get 256 oz., about 10 times your calculated value for 100% bleach. using 1% bleach gives 2616. not exactly linear, but in the ball park. note the changes in calculated ozs of bleach as you increase the bleach conc from 50 to 60 to 100. not linear at all. stick to typical ranges of actual bleach and you should be much closer to getting what you want.
 
mikemass said:
You agree with that assessment right?
Click to expand...

I agree with that assessment. I think I may have also found the potential "smoking gun" of the calculator being incorrect at values I'm trying to simulate. With the other values remaining constant, if I input 10% bleach solution into the calculator, it indicates 256 ounces is required. If I up the value to 20% bleach solution, the required ounces drops to 128 ounces as expected. However, 40% solution only drops to 68 ounces instead of the expected 64 ounces. Likewise 80% only drops to 49 ounces instead of the expected 34 ounces. It seems that right around 75% solution the required ounces bottom out and actually start to increase! There's definitely something wrong with the calculator...

Given that anything above 20% is basically unattainable, I guess I can live with that =)

Now to figure out the formula given the watered down nature of household bleach....

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domct203 said:
...if it is still standing during said natural disaster, or not frozen over during said winter storm LOL.
Click to expand...

Haha, I hear ya! I doubt I'd be worried about the pool at all... I guess a good portion of the drive to find a formula is the desire to not become reliant on technology. Kids these days can't write a simple email without asking Siri a dozen questions... =)
 
cdoc83 said:
.........Haha, I hear ya! I doubt I'd be worried about the pool at all... I guess a good portion of the drive to find a formula is the desire to not become reliant on technology. Kids these days can't write a simple email without asking Siri a dozen questions... =)
Click to expand...
So, you know my daughters? LOL.

Dom
 
Alright, contacted a more science inclined friend, PPM, or parts per million, is actually a MASS ratio, not a VOLUME ratio... Water is commonly regarded as 1 gram per milliliter. Trying to see if we can find the mass of the chlorine part of the sodium hypochlorite....

I'm starting to think pulling the javascript from the calculator might be easier...
 
I'm with domct203 on this.

I have a post-it note on the inside of my test kit listing how much it takes to raise FC 1ppm for the three most common bleach percentages (8.25, 10, 12.5) and for lowering pH by 0.1 using 31.45% MA for my pool volume.

Two things I never have around the pool - anything glass and any portable electronic devices. Having either near my pool can have unpleasant results, to say the least.

I think PoolMath is weighted for the most commonly available chlorine types and concentrations. PoolMath is kept up to date. I would certainly shy away from the Pool Calculator and it's associated app as it hasn't been updated in several years.
 
proavia said:
I have a post-it note on the inside of my test kit listing how much it takes to raise FC 1ppm for the three most common bleach percentages (8.25, 10, 12.5) and for lowering pH by 0.1 using 31.45% MA for my pool volume.
Click to expand...

Yeah, that totally makes sense. I'll probably leave it to that for now. Another part of figuring out a formula is to use it in other areas as well, such as creating the CDC recommended 200ppm solution for disinfecting after a flood or creating a 100ppm shock treatment for a cistern well, or whatever else may arise that I can't plan for ;)

Thanks all for the discussion, fun stuff!! I guess it's back to work for now...
 
In case it's of any use for anyone else, here's the formula used by the calculator:

([Chlorine PPM Target] - [Current Chlorine PPM]) × [Number of Gallons] ÷ {(75.71 × [% of Bleach]) + (.746 × [% of Bleach] × [% of Bleach])}

This formula was also verified by my science friend as "close enough" =) Enjoy!
 
Someone posted a excel spreadsheet where you enter your pool gallons and it gives ozs of different percentage of LC to add for different PPMs. Cant remember where it was. I edited it printed it out and taped to the inside of my kit.
 

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