@CarlD: Liquid Chlorine testing

[dhanger]

Carl:

I've seen you mention something similar to the below quote several times-

I generally use a higher qual LC that claims 12.5% but always tests at 14%

I'd like to know how you go about testing the percent value of the chlorine you buy. I could probably figure it out, but I'd end up asking anyway just to confirm. Reason I ask is because I just popped in to a local pool supply discount shop, and he mentioned that he gets Hasa brand LC from the local manufacturer in Eloy, AZ, and it comes in at 17% strength. He sells it for 13.90 for 4 gallons, which seems like a pretty good deal if the strength is legitimate. I haven't seen that high a percentage mentioned here or anywhere else, and I'd like to be able to verify it for myself.

Thanks,
Dan

[CarlD]

Put ten liters of tap water ( That's 5 soda-bottles full) in a 5 gallon bucket.

Test that water for chlorine using the FAS-DPD test to get a chlorine baseline (you may have some).

Then I take a 1 ml eyedropper full of the LC or bleach I'm testing and put it in the bucket and mix it up.

(1 ml in 10 liters of water is the same as putting 1 gallon of LC in a 10,000 gallon pool -- it's 1/10,000th. )

I then measure the bucket with the FAS-DPD test just like pool water. Of course, subtract any chlorine you measured in the tap water.

I use a glass eyedropper so it will hold up. Pharmacies sell them.

[dhanger]

Ok, so if it's supposed to be 17%, then I should get a reading of 17 ppm, correct? Hey, my son's the math major, not me.

So, after my first post I decided to check out the Hasa website and their MSDS page, I didn't find any of their sodium hypochlorite products that showed any higher than 12.5, which until now is the highest I've heard of. I won't be getting this stuff until next week so it will be a while before I can confirm it. I guess I'm wondering if this guy is blowing smoke, are higher concentrations even allowed? I know you've measured 14%, but it's sold as nominal 12.5, right?

Dan

[CarlD]

Yup, they generally sell it as 12.5 or even 10%. That's to allow for the breakdown. Higher concentrations of chlorine break down faster to lower concentrations. So if they bottle 14% and it breaks down to 12.5% after a few weeks they haven't lied about their product. Still, breakdown is inevitable and unavoidable.

The main reason to test your higher concentration LCs is to see if it has fallen below the rated concentration and then use it up, adjusting your amounts accordingly. I'm not a fan of defending pool stores but in all fairness to them when they are selling gallon jugs of 12.5% and maybe they test at 10 or 11% they aren't cheating you. It's very hard to control it any more than that.

[jhm]

Can you do the same or similar test for MA? The pool store claims they have a much greater strength than Home Depot (which I know a couple years ago the strength was cut in half, but not the price). However, none of the acid I use these day seems as strong as the stuff I was using 5 years ago.

[CarlD]

I have no clue how you would test the concentration of Muriatic Acid. Nor if you can do it with pool tools.

[Sponge1971]

(1 ml in 10 liters of water is the same as putting 1 gallon of LC in a 10,000 gallon pool -- it's 1/10,000th. )

Carl,

I'm prompted from the thread I started about cost vs % and the 'discrepancy' issue that rose up there.

From your suggestion, there, I did my first "Carl Method" testing and I liked it...and it made sense to me...and the more I thought about it...It's just like getting a test result from a 10liter pool. The ratio of the 1ml vs 10liters is linear. I could do the test at 5x the original volumes and get the same effective linearly higher result. Which was how I calc'd how much of my 'tested' chlorine I needed to add to my poo's volume, to get the rise I wanted...

Anyway, sorry...I'm long winded...I have a stoopid question:

I'm certain '1 PPM' means: One Part Per Million (all of the same size parts)
so...
how can the 'result' of the 10liter test be a 'PPM' value, when the basis for this method's ratio is 1 in 10,000...and not 1 in 1,000,000? The number will be the same but the decimal point is wrong...right?

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I think I just figured it out! (but I'm not deleting this...it took me 20 minutes to get this far...so I'm hunting for confirmation now...)

The 10 liter test result isn't a PPM value. It really is only a PP10,000th value.
But...Carl never "said" the test result would be in 'PPM'. The test is to determine the % concentration of the bleach being tested.
A % is a 1/100th value...and 10,000 is 1/100 of 1,000,000!
The DPD-FAS result really is a PPM value, of what's going on in the bucket. But...the ratio of bleach to water is jacked up by 100 times...and nobody told the FAS-DPD...and because of that 100x-ing the PPM number turns into a % number!
VERY CLEVER and damn easy!

Now I understand what giroup01's point is...Your test assumes a 1:1 relationship between PPM and % Sodium Hypochloride. He's saying that ratio isn't exactly 1:1, but that the PPM of chlorine available is slghtly lower...and that will fudge your results.
I see his point, purely...but, as I rambled on in that other thread...I'm testing my pool to +/- 0.5PPM resolution. I'm willing to bet that variation won't manifest enough error...at 'normal' % concentration values. I guess If I wanted to be a purist, I could just chuck in that 'factor' in the final PPM vs % result. I think I'll tinker with this...just for gags...

[CarlD]

Hi Eric,
Remember the formula:
((1,000,000/pv) * (conc) * (L) = ppm

1,000,000 = one million
pv = Pool Volume in Liters
conc = bleach concentration AS A DECIMAL, so 6% is .06, 5.25% is .0525, and 12.5% is .125
L = amount of bleach added, in Liters.

So if you have a 10,000 liter pool, and add a liter of 6%, the increase in PPM is....6!
If you have a 20,000 liter pool and add 1 liter of 6%, the increase in PPM is 3
15,000 liters, 4.5.

Using this trick I just reduced PV to 10 and L to 1ml 1 ml is 1/10000 of 10 liters, but 6% of THAT is 6/100ths of a milliliter, or....6 millionths of the 10 liters, ie, 6ppm.

BTW, I do all my pool calculations in gallons of water and bleach, but it doesn't matter. The ratios are the same.

So, if the % is 10.8, but the measured is 10.3ppm, do you REALLY need to care? I defy ANYONE to measure their pool's current volume that accurately.
Think about it: If your pool is 40'x20' and rectangular, a difference of just ONE INCH in depth is 500 gallons (almost 2000 liters). One inch. How many let their pool drop a few inches before adding water?

So...my method is a nice quick and easy way to determine the pool store that sold you 12.5% LC really sold you old junk that's barely 5%. If it's close to 12.5, you are good. What's your alternative? Hire a lab to test it for you? Seems pointless.

Finally, the ONLY risk of overdosing your pool with chlorine is you MAY bleach a vinyl liner. All the calculations in the world don't change the recommendation that when adding chlorine, adding a little more than you calculate is a GOOD thing, but with everything else you want to add LESS than you think you need and re-measure.

Carl

[waterbear]

One other thing to consider if you are looking at "pool store liquid chorine", if it is sold in carboys that are filled on premise then it is being delivered to the store via tanker and stored in large tanks on site (I used to work in such a store and I can tell you that there is no greater joy than refilling carboys in the middle of summer in the hot Florida sun!). One time when reordering the bulk chlorine from our supplier I asked then if it was actually stronger than 12.5% (since I had notices that FC were a bit higher then expected in some customer's pools) and they said it was closer to 17% when it left their facility to compensate for the loss of strength on storage that the 12.5% was a minimum of what the product would be.

[CarlD]

Evan,

That sound's about right. The shop were I get my LC has a very high turnover rate (plus the sun isn't quite so intense in NJ as it is in Fl, even if we are 15 degrees hotter and 20% more humid!) so I'm not surprised that it's still in the >12.5% range when I check it. They are one of the few that makes serious $$$ on LC, but that's because they go through SO MUCH of it, pallets and pallets of carboys per week.

Carl