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

[giroup01]

You need to compare the quantity needed for 1 ppm in a 10 000 liter pool, you can take it from there.

The WalMart stuff, you need 250 mL of 4%, cost per ppm, $0,10
The pool store stuff, you need 83 mL of 12%, cost per ppm $0,05.

If you think of "cost per ppm" then it becomes very easy to determine if the price is good or bad or average.

Walmart probably has higher turnaround than the pool store, you could ask the pool store to check the actual chlorine content of the 12% stock (only 0,5 mL is needed if you use the Taylor bleach kit).

12% degrades much faster than the 4% stuff.

Bleach isn't necessarily cheaper by the way, Trévi has (had) cal hypo, 14 kg of 65% for $38, you need 15 grams for 1 ppm, cost per ppm $0,04.

I keep all that info in a spreadsheet, the Walmart bleach is actually one of the more expensive solutions to date, Trévi being the least expensive.

[CarlD]

1 milliliter of 12% added to 10 liters of water is the same ratio as adding 1 liter of 12% to 10,000 liters. (I usually do it in gallons but the ratios are exactly the same).
So test your tap water and get a baseline FC reading.
Then put 10 liters of tap water in a bucket (since even in the US 2-liter soda bottles are everywhere, 5 of those works).
I use a drug-store eyedropper (glass, of course) with measures on it already for 0.5 and 1.0 ml. Add 1ml of 12% to the 10 liters and mix it up. Let it sit for 10 or 15 minutes.
Measure with your K-2006 FAS-DPD test to find the chlorine level, and subtract the FC of the tap water.
The resulting measure is the actual concentration of your liquid chlorine.

(This comes from the formula for ppm: Parts per Million.
((1,000,000liters/10,000liters [pool volume]) * .12 * #liters of chlorine) = ppm, where .12 is 12% strength liquid chlorine. You can substitute .0525, .06, .105, or .125, depending on the claimed concentration. # Liters is assumed to be 1, but can be more. Again, it works just as well if you substitute gallons for liters everywhere. I simply reduced it from 1,000,000 liters to 1,000,000 milliliters, pool volume to 10,000ml and # Liters, becomes #ml.)

Carl

[Sponge1971]

Excellent Guidance!

My tap = 1.2ppm (did the high precision 0.2/drop measure)
My 10l & 1ml sample (blended and 10mins) = 11.5ppm (0.5/drop)

Bleach concentration = 11.5-1.2 = 10.3ppm = 10.3%

I guess that's not too bad. I never realised the conc could drop so much. I'll have to check again in a month, just to see the rate. There could/will be a point where other options would be more cost effective...depending on my consumption.

thanks Carl!

[CarlD]

Glad to help!

The higher the concentration the faster it can break down. Apparently, the solid blue carboys LC is sold in here in my area is really good at protecting the stuff.

Carl

[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.