New China Shop Topic: How Accurate is the Pool Calculator?

[CarlD]

Richard, that's the first good defense I've read of the deviation in the Pool Calculator from the formula. THAT is an explanation I can accept. It also points out there is a potential inaccuracy in the FC section. Naturally, neither the PC nor the formula take into account any degradation or breakdown in the chlorine over time. I'm confident your coefficients are correct but where do they come from. BTW, how many grams/mole are there in CL2 and NaOCl?

Madwil, I suppose it's a difference of definition but the VARIABLE "Concentration" must be defined as 4 digits to the right of the decimal point because available VALUES can use any of the 4 places...LC would be expressed as .125, while regular bleach is .0525. Each uses only 3 digits, but 4 are still needed.

Carl

[madwil]

That's why it's a place holder...
0's at the end of a number, without decimal places, are not significant.
0's after the decimal, before numbers, are not significant if 0 precedes the decimal.
Otherwise, you could call 2 ppm .000002 and say it's 6 sig dig, when it is only 1!
Consider scientific notation- a.bc x 10 to n power- a.bc is sig, not the location of the decimal point, with regards to accuracy/precision of measurement
When you mult/div numbers, the lowest number of sig dig in any of the factors is the number of sig dig in the product
When you add/sub, the number with the highest multiple of 10 becomes you last sig dig (1,250 + 2, is still 1250 for significance...)

[waterbear]

People, we are losing sight of the fact that we are talking about a swimming pool and the amount of water in the pool needs to be accurately known (and not rounded off to the nearest 1000 gallons or so) or this all become moot.
It's a swimming pool, not a science experiment and in the real world we are just splitting hairs here that are not important. Now I am the first one that insists in precision and accuracy when doing a scientific experiment (lest anyone forget I have a very similar scientific background like chem geeks) BUT you need to take in account your largest margin of error (which in our case would be the volume of water in the pool) and not try and get a precision smaller than this limiting factor because it is invalid! Yes, I know that errors are cumulative but if we are talking about errors that differ on such a significant order of magnitude they become insignificant!

We also have to take into account the precision of our testing methods and any errors introduced by our testing methodology.

What it boils down to is that the 'guestimate' that CarlD provided of one gallon of liquid chlorine adds approx. it's strength of FC to 10000 gallons of water is about the amount of precision that we can expect in real world situations of pool maintenacne and it is most certainly close enough for our purposes of maintaining a pool.

(If anyone is old enough to remember using triple beam balances or balance pans remember that the weight is taken after three equal oscillations of the pointer and not when the pointer had come to rest. This is my point, you have to realize what the limit of your precision is.)

[Watermom]

Y'all just need to go swimming and have some fun.

[CarlD]

You don't think arguing is fun???? That's why we have the China Shop.

There's difference between measuring with something you know is off and correcting for it: "My speedometer always reads 5mph fast"
and something you believe is correct and isn't "But Officer, I had it NAILED at 55mph on my speedometer, not 65".

Can't go swimming. It's nasty, cold and raining. Therefore, arguing is a valid alternative source of fun!

Carl

[waterbear]

Can't go swimming. It's nasty, cold and raining. Therefore, arguing is a valid alternative source of fun!

Carl

Explains everything!
Beautiful sunny weather here, been swimming for several months now and the pool stays a comfortable 85 degrees without my heat pump running! Getting ready to jump back in before I start grilling!

[chem geek]

BTW, how many grams/mole are there in CL2 and NaOCl?

CL2 is 70.9064 g/mole while NaOCl is 74.44 g/mole. That's where those numbers came from in the formula in my post.

[PoolDoc]

Hey All, Richard;

Tell me that you have taken into account the time and temperature related decomposition of bleach? Odds are that 6% bleach started as 8 or 9 in hopes it would still be 6 when YOU got it. If they filtered the nickel and iron out, and kept it cool, it probably IS 6% or more. If not, well, not.

Ben

[chem geek]

The idea is just to start out with what is the most likely value -- that claimed by the manufacturer. As I wrote, it's not that important, but if you're going to have an automatic calculation you might as well start with the correct intended number. Errors accumulate so there's no point in starting with something you know is likely to be wrong.

6% Bleach doesn't degrade very fast because the rate of degradation goes roughly as the square of the concentration. 12.5% Chlorinating liquid degrades more quickly. See the chart at the bottom of this page. As for impurities, you'll note that this manufacturer does remove catalyst metals from their source water and I checked with Hasa on the West Coast who is the source of the chlorinating liquid I use as well and I also checked with Clorox about their bleach. Most of the big players take care to produce a quality product. I can't speak for the off-brand Ultra bleaches.

[PoolDoc]

Hi Richard;

I was sort of teasing, though I do think excessive precision is a bane of good pool care.

That said, because I bought, sold, and delivered 15% bleach for 15 years, I investigated bleach stability as much as I could, given the paltry Internet resources available at the time.

One possible oversight in your remarks above: according to the man whose company* made the bleach I started off with, the significant source of metal contamination of bleach was not the source water, but the chlorine liquid. Nickel and some other trace contamination originated in the manufacturing process; iron in the transport and piping process. Producing low-metal bleach required post manufacture filtration of the bleach itself. Fully effective filtration apparently results from the use of bleach tolerant micro-filtration.

So, based on what I was told, a bleach manufacturer who's hyping source water filtration is really just dodging the question.

The first company I purchased from did not even make high purity bleach at the time -- their business was build on selling to the cotton chenille makers in Dalton, Georgia, and it was a fast delivery, high turnover process. By the time I was dealing with them, their business was with cotton sock makers in Alabama. But even in summer, the bleach didn't decompose faster than their 2x weekly deliveries. The second company did make high purity bleach, but only on an erratic schedule, and my purchase volume wasn't large enough to change that schedule. However, water filtration would have been a non-issue for them both, since they were using limestone spring or well water.

Ben

* His father-in-law revolutionized bleach production -- so I was told -- by dumping sugar in bleach, resulting in the formation of gluconic acid which chelated the iron in the bleach.