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

[CarlD]

"Fess up.."

OK. Full Disclosure: I confess. I really do NOT care if it's 2.3 or 2.4!

Saying that, I'm well aware of all the other variations. In fact, I spelled them out. I know how to test for chlorine concentration (I've posted the method a number of times). I know how to calculate pool volume (most use 7.5 gallons for gallons/cubic foot but the more precise number is 7.48). I even realize that drop size changes and the recommended way is to hold the bottle exactly perpendicular.

But I have shown how two separate rounding functions used consecutively have generated an inaccuracy that results in .1 increase above the correct rounded figure.

Is accuracy to 4 decimal places necessary? Sounds petty to say "yes" but it's not. Bleach concentrations go into the formula out to 4 decimal places routinely (5.25% bleach is .0525 in the formula).

We estimate pool volume. We estimate bleach concentration. We even estimate amount of bleach. These are all, to the statistician, known levels of error or "noise" The formula should NOT introduce another level of "noise" if it is not necessary.

Your statement at the top "YES. It's accurate." needs to be amended: Yes, it's accurate to 1 part per million. This is certainly true and I have no problem with that.

However, the calculations CLEARLY show that it is NOT accurate to 0.1 part per million.

Carl

[AnnaK]

Which of the water balance parameters require 0.1 ppm?

Or, coming at it from another way, do the many variables we've both enumerated need an accuracy consideration to 0.0001 part per billion? Can we even measure that?

[CarlD]

Which of the water balance parameters require 0.1 ppm?

Or, coming at it from another way, do the many variables we've both enumerated need an accuracy consideration to 0.0001 part per billion? Can we even measure that?

Don't you mean 1 part per billion (1/1000 of a million).

Of course none of the majors do (pH doesn't really count). The lowest we EVER need to go is .2 (useful if CC is not clearing properly).

But you are defending a known, fixable inaccuracy in the system.

Carl

[Manslick]

What if 6% chlorine is 5.9%. OMG.

[AnnaK]

The inaccuracy of the bleach calculations within the Pool Calculator is not really germane within the context of usage.

The defense rests. The defense is just about to take her dogs swimming in a pool that may well be off by a couple parts per gazillion (that's 10 to the nth). The defense does not plan to agonize over that. Instead, she plans to dose herself with an imprecise amount of Margarita, accuracy be gosh danged.

Have a great weekend!

[Manslick]

You go girl.

[CarlD]

The reason I put this in the China Shop was so that it could be batted around and argued about. I do not like tools I know are inaccurate, and I can guestimate chlorine usage just as quickly and accurately with the Rule of Thumb--and I don't need to be near a computer to do it. I can estimate MORE accurately with just a calculator even on a cell phone.

This is not a statistical error. That would be simply noise and of no concern. It is a systemic error which is a whole 'nother kettle of fish.

The Pool Calculator generates other recommendations, including amounts of Borax and other additives. What is the accuracy of THOSE estimates?

I am reminded of Doc Brown's 2 story tall ice machine that makes one cube of ice.

Remember: The China Shop is for arguing. If you don't want to, you don't have to.

Enjoy swimming with your dogs (BTW, they are something like 30x dirtier than a person who gets in your pool. So 2 dogs is like a load of 60 bathers) (according to our vet who does water-therapy for dogs).

Carl

[waterbear]

The pool calculator is a useful tool but ANY method of calculation of chems DEPENDS on ACCURAATELY KNOWING THE AMOUNT OF WATER IN THE POOL AT THE TIME OF CALCULATION!
The Pool Calculator and BleachCalc (remember BleachCalc?) both produce very similar results (certainly close enough for pool maintenance...it's not rocket science after all--its a swimming pool!) except for the borate calculation where it is known that BleachCalc has a major error in the algorithm used to determine borate concentration.
If you want more precision and accuracy then Chem Geek's "monster" spread sheet is around (but I find it intimidating and a bit scary and I am VERY computer literate!) However, unless you are doing theoretical workd on the effects of chemical additions in a pool you once again do not need this kind of precision.
Personally I like to use the Simplified Formulas for Chemical Additions from OnBalance for calcualting chems since all I need is a printout of their Formula Numbers and a calculator, which is much easier to carry to the pool than a computer or even a phone!
They even have a method to chemically determine the volume of a pool that I have used several times and it certainly gets you pretty much in the ballpark, even for oddly shaped pools!

For a Newbie, I think BleachCalc is the easiest to use but the Pool Calculator that Jason from TFP put together has a bit more info for more advanced users.
BUT, if you don't accurately know how much water in the pool then NONE of these tools are going to be very useful at all.

[waterbear]

The Pool Calculator generates other recommendations, including amounts of Borax and other additives. What is the accuracy of THOSE estimates?

I have used all the calculations on it and have found it close enough for government work. so to speak. The Borax calc is very much on the money but then again your don't need that much precision. 60 oz by weight of borax and 30 liquid oz of muriatic acid will raise borates to approx 50 ppm in 1000 gallons and keep the pH pretty close to where you started. You really don't need to be more precise than that, IMHO.
If you are talking about borax for raising pH then NO calculator is going to tell you how much to add. You will need to use a base demand test and use twice the weight of borax as you would soda ash for a specific pH rise as determined by the test. Not rocket science and a lot easier than adding a bit and waiting and testing and adding a bit more and waiting and testing until you 'creep up' on your target pH.

[AnnaK]

Enjoy swimming with your dogs (BTW, they are something like 30x dirtier than a person who gets in your pool. So 2 dogs is like a load of 60 bathers)

Wouldn't that depend on the size of the dogs? And their breed? A Chinese Crested is probably a lot cleaner than a bunch of . . . oh, say, Belgians.

I do appreciate the concept of the China Shop but I'm too old to argue. I've learned that when I'm right, I'm right.

Those Margaritas were lovely