Need 2nd Opinion on % vs Volume vs $ calculation/assumptuion

[giroup01]

On the bleach bottle you read the % concentration of sodium hypochlorite.
What you are measuring is the concentration available chlorine content.

Not the same thing.

[CarlD]

On the bleach bottle you read the % concentration of sodium hypochlorite.
What you are measuring is the concentration available chlorine content.

Not the same thing.

What is the point of that?

The whole point of the calculation is to determine how much available chlorine the Bleach/Liquid Chlorine will deliver. Ultimately, that's what you need to sanitize your pool, and the concentration is merely a guide to get you there.

Parts Per Million added = (1,000,000 / pool volume) * (Bleach or LC Concentration (as a decimal)) * (amount of bleach or LC used)

If you add 1 ml of bleach or LC to 10 liters of water the resultant Parts Per Million measured, less the public water's residual FC is = to the concentration of the bleach bottle.

What's the problem?

Carl

[giroup01]

The point of that is that you'll read on the jug "Guarantee: Sodiun Hypochlorite: 10.8%" then when you test a fresh batch you'll come up with "Available chlorine content" of 10.3% and think the batch is not fresh.

The original poster is looking at 12% sodium hypo from the pool store and measures the chlorine content at 10.3% then comments "I guess that's not too bad. I never realised the conc could drop so much."

The 12% is sodium hypo concentration, the 10.3% is chlorine content, technically he's comparing two different things. (He also mentions "Bleach concentration = 11.5-1.2 = 10.3ppm = 10.3%", that's not bleach concentration, that's active chlorine concentration).

And also, keep in mind the "parts per million" is a weight to weight measure, you must consider the solution density in your formula. 12% bleach is heavier than 3% bleach.

All these details add up.

[Sponge1971]

Don't want to start a battle here...and I'm absolutely not qualified to really understand the points being made. Formulas I can handle...

For what it's worth...I wanted to add +2ppmFC to my pool today (reading was3ppmFC). ThePoolCalculator said: "16oz of 10% bleach will raise 2ppmFC". I mixed in 2cups of what I have, in my yellow jug, and tonight my reading was up to 5ppmFC.
For What It's Worth...I use a Taylor k-2006 and run 10ml (0.5ppm/drop) samples on my pool water. I 'did' do a 0.2ppm test on my tap, because I 'know' that one is pretty low. As for Carl's test method, I started with a 0.2ppm test, but gave up after 20drops. I can't afford to waste my reagent like that. So I ran a 0.5ppm test on that water...so there is a +/- 0.5ppm resolution on that "%conc" (or whatever) reading.

To be fair, I never asked TheCalc what 12% amount I needed to go +2ppmFC...and with only a .5ppm resolution...I might not have noticed the difference anyway.

To me, Carl's testing method seems to work and makes sense since it's a titration method, just like the FC sampling I'm doing anyway. If this test ultimately gives me a reliable way to ensure proper dosing...I'm happy with it.
The way I understand it:
(I rounded the numbers, and ignored background FC, for simplicity)
- 1ml of my yellow jug = 10ppmFC in 10liters of 0ppmFC water.
- I only want 2ppmFC so I only need 1/5ml...so then:
- 0.2ml of my yellow jug = 2ppmFC in 10liters of 0ppmFC water.
- My pool is 20000liters (or...2000 x 10liter buckets)
- to get + 2ppmFC in my pool I need to add 2000 shots of 0.2ml from my yellow jug.
...or 2000 x 0.2 = 400ml (13.5oz) from my yellow jug.

That's close enough for me, and it seems to have worked...


So...does your's disagreement matter? ...since all this 'stuff' is labeled as % anyway? Even if the testing doesn't work out to a 'true %' reading...it is an indication of some sort...and that 'relationship' will translate across all the different 'stuff' available. 12% is Carl's 10...4% is Carl's 3.33333 ....as long as it's consistent...it's a reliable yardstick.
...let's not argue about it, if it's only a 'tomato' or 'tohmato' type of thing...
-or-
let's get el-super-brain ChemGeek to referee this discrepancy...and help nail it down to ultimately come up with a take-it-to-the-bank solution to help everybody verify their 'stuff', to ensure cost effective dosing, maybe help protect us against unscrupulous vendors and just pile on another good reason to be part of this great forum and what it stands for.

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My whole point for this thread was to try and ensure my thought process was accurate in trying to determine the most cost effective way to chlorinate my pool.
As I have thought more about it: 'splitting hairs' could come down to how much time & gasoline I have to spend and how much storage space I need to achieve this chlorination. (Walmart is on my way home from work, would only cost me 15minutes of 'free' commute time, but easy-to-handle jugs take up valuable space in my shed...and my recycle bin.)(The Pool Store is completely out of my way, pretty much for any travel I do. So that's a 30-45 minute round trip + gasoline to fill up (a $15 cumbersome-to-handle jug I had to purchase) x-number of times a season, but is pretty compact in the shed.) There's still a few hairs to split if I want to get anal about it.
I *really* should grab one of those Walmart jugs and run Carl's test on it, to see what it is...and compare it from there. I'll never be able to control the 'freshness' factor and I'm certainly not going to test each jug...but maybe after a few random tests...I can get comfortable with what each option offers and put that part of the equation to bed. Also, I'm a first-timer, at the end of the season, with minimal bio-load...and I 'still' haven't made up a log book....so I can't reasonably expect to determine the frequency/amplitude of chlorination...which will have a huge impact on the whole 'hair splitting' process.
...and then...there's this whole "cal hypo" option that giroup01 mentioned...and the great "cost per ppm" comparison suggestion...which I think I'm doing by going with Carl's method. This way, I can somewhat-reliably nail down how much of "whatever option" I need to raise my pool by 1ppm...and see it's ultimate cost.

I think my head is going to explode

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Oh...and thanks again for all yous's help. The members of this forum all rock! I especially appreciate the intelligent on-going discussions and apparent lack of ego...unlike the various motorcycle forums I used to frequent.

[waterbear]

I'm with giroup01 on this. You are comparing apples and oranges and it can and does matter.

[CarlD]

And what do these details add up to?

It still comes down to putting enough chlorine into your pool to make it sanitary. Is it going to matter if you think one gallon of LC is going to add 10.8ppm to 10,000 gallons when it only adds 10.3? What really matters is if the stuff is still good and relatively close to what it's supposed to be.

I'll bet not one person in 100 knows within 200 gallons how much water is in their pool. And if it's anything bigger than a donut, I'd guess that variation would be 500 gallons. I'll bet nobody here knows it that accurately. We know APPROXIMATELY how much water is in our pool. And, when it comes to shocking a pool, it doesn't REALLY matter if the pool is 19,000 gallons, 20,000 gallons, or 21,000 gallons. You can safely use 20,000 gallons for all your calculations.

So...where does the problem with this measure of concentration crop up? Where is the bleach calculator formula wrong? Why is it wrong? More importantly, is it wrong enough to matter? Or is it a good enough approximation?
(we know Isaac Newton's laws of Physics are fundamentally wrong and that Einstein's Relativity fixes those problems, but Newton's physics is STILL a good enough approximation to use to fly a probe past Pluto without resorting to Relativity. See my point?)

More importantly: Can YOU come up with a better method of determining if your bleach / liquid chlorine is still good?
By better I mean something a homeowner can practically implement, not something that needs a sterile lab with people in white coats.

Carl

[aylad]

This is bordering on China Shop material......the OP is satisfied with the information that he has. So if y'all want to continue the debate, please take it to the Shop!!

Janet