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

[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.

[HofstraJet]

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.

So The Pool Calculator's suggestions for how much Borax to add for a specified rise in pH are incorrect?

PS - love the academic debate. Keep it up!

[waterbear]

Acid and base demand cannot be calculated without a chemical test since they depend on other factors such as TA and temperature and how fast the chemical is added. (for example muriatic acid will have an almost instantaneous effect on pH while cyanuric acid, because of its slow dissolving nature, will not have a appreciable MEASURABLE effect since the slow drop in pH that occurs as it dissolves will be offset by the bicarbonate buffer in the water and the pH rise from outgassing of CO2 and the drop in TA that it will cause is going to be smaller than the precision of our TA test.)

A calculator like the pool calculator or a treatment table can only approximate how much of a pH rise or drop a certain amount of a chemical can cause that may or may not have ANY basis in reality! IF your pool is in what is considered a normal range of balance and temperature then the results can and will be off, particularly for large changes in pH. In fact, here is a direct quote from the pH section of the pool calculator:
Note: pH calculations depend on TA and Borate. Results are approximate and can be off significantly for large pH changes. Changing your pH will also change your TA.

IF you want a more precise way to determine how much of a chemical you need then do an acid or base demand test! (since base demand tests are set up for soda ash--sodium carbonate--it is lucky that twice the amount of borax by weight--sodium tetraborate decahydrate--produces about the same pH rise so you just need to double the weight of soda ash when substituting borax for pH increasing.

[chem geek]

As waterbear noted, knowing an accurate amount of acid or base to add to move to a specific pH is best determined through an acid/base demand test such as found in the Taylor K-2006 test kit. However, The Pool Calculator does a decent job estimating the amount and accounts for the various buffer systems in the water including carbonates (TA), borates and CYA. However, at the time the calculator was made the accurate calculations in my spreadsheet were too complicated to put into the calculator so Jason created tables/formulas that approximated the effects. Since that time, I've found simpler formulas for the accurate calculation and this is discussed in the thread pH Buffer Capacity. Unfortunately, Jason sold The Pool Calculator to pSIFlow Technology Inc. and they don't seem to be doing any maintenance on it.