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

[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.

[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.