The Great Tetraborate Experiment!

[nater]

Great Experiment Evan!

I've been running 30-50 ppm Borates this year, and agree with your assesment on the feel and look of the water.

What would you impose for an upper limit on Borates? Is there a point of dimminishing returns above 50 ppm? What about 100? (Man Logic at its best; if 50 ppm is good, then 100 ppm must be better)

[waterbear]

All the info I have been able to find on tetraborates seem to indicate that 30 ppm is where the algaesatic properties become effective and that after 50 ppm there seems to be not that much additional benefit. I don't know about any other implicatons of running a higher boron level.

[waterbear]

Weekly pool test....not much had changed
FC 5.0 ppm
CC 0 ppm (no change)
pH 7.5 (Usually up to about 7.6 after a week)
TA 120 ppm (before stabilizer correction) (no change)
TA 97 ppm (after stabilizer correction) (no change)
CH 220 ppm (no change)
CYA 70 ppm (no change)
Salt 3600 ppm (once again using the display on the Aqualogic.
Salt 3550 ( AquaChek White salt test strip)
Borates 50 ppm

Pool is clear, clean, and sparkling. Have company for the week. My Nephew, his wife, 1 grand niece and 2 grand nephews are coming in Sunday so the pool will be getting a lot of use. We will see what happens.

[waterbear]

Okay, another week has passed (2nd week of experiment) and I had family visitng (Nephew, his wife, grandniece, and 2 grandnephews) this week so pool got constant use daily! Here are the numbers:

Borates 50 ppm
FC 5.5 ppm NO CHANGE (I lowered my SWG output very slightly after the test and will see where I end up in a week. I had bumped it up a bit a few weeks back because we were getting a lot of rain)
CC 0 ppm
pH 7.6 (this is amazing! By the end of 2 week my pH is usually at 7.7-7.8. I also started this experiment with a pH of 7.4 and usually lower my pH to 7.2 when I add acid to my pool! Richard, care to comment on this?
TA 120 ppm (I have had the spillover and waterfalls running almost constantly all week for the kids.) NO CHANGE
Adjusted alk 97 ppm NO CHANGE
Calcium 220 ppm NO CHANGE
CYA 70 ppm NO CHANGE
Salt 3600 ppm (readout on AuqaLogic)
Salt 3600 ppm Tayor K-1766)
Pool is still clear and sparkling. My nephew's wife commented on how she didn't need to wash her hair after swimming. She asked what I put in the pool because she said she usually has to shampoo after swimming or her hair dries flat. I told her it was because it was a salt pool. She told me she's been in salt pools before and still needed to shampoo. I just smiled at her

So far my pH seems to be more stable than usual. That is what I was hoping for. We shall see if it continues on a regular basis. I guess the real test will be when I need to lower the pH with acid! My grandnephews and grandniece told "Uncle Evan' that my pool didn't make their eyes burn even when they spent most of the day in it ....they liked that! Can't comment on whether that is from the borates or just because I keep on top of the water. I have done nothing to the pool the week they were here except test the chlorine levels Wednesday night because I suspected my 3.5 year old grandnephew went #1 in the pool! There was no CC.

I also tested the spa. The only difference is that my FC was 10.5 ppm. I am not surprised since the kids spent a lot of time in it and the SWG does run when the spa is on. I turned the heater way down since they were spending so much time there. They loved the bubblers and jets! When the spa wasn't running it was in spillover mode so it and the pool were being chlorinated to to same level. I turned off the spillover the last day they were here (thursday) and they were in the spa for several hours with it running so I am not suprised the FC in the spa rose above the normal 6-7 ppm it stays at.

The experiment continues......will report in another week.

[chem geek]

Boric acid acts as a pH buffer, but not as much as the carbonate buffer. However, though I have put in the stoichiometric info into my spreadsheet so I can tell you how much boric acid is needed for a certain ppm (and vice versa), I don't have the equilibrium equations put in yet so can't tell you the precise buffering effect. At some point I will and will let you know if that's what's going on.

Your TA of 120 and pH of 7.6 is consistent with relatively stable CO2 outgassing. You might consider lowering the TA to 100 to see if that slows down your pH rise and acid usage even more (if not, then perhaps your pH rise is due to some acidic substance entering your pool -- rain, bathers, etc. -- though I'd like to eliminate the CO2 outgas as a possibility first). Other than that, it sounds like this experiment is an absolutely resounding success! I'll be checking out both the addition of salt (I don't have an SWG yet) and boric acid since both seem to have benefits.

Richard

[waterbear]

Boric acid acts as a pH buffer, but not as much as the carbonate buffer. However, though I have put in the stoichiometric info into my spreadsheet so I can tell you how much boric acid is needed for a certain ppm (and vice versa), I don't have the equilibrium equations put in yet so can't tell you the precise buffering effect. At some point I will and will let you know if that's what's going on.
According to the info from Proteam about Supreme 30 ppm is supposed to increase TA 10 ppm. Is this info helpful?


Richard

Also, wouldn't the buffering effect from borates be immune to the outgassing of CO2?

[chem geek]

Yes, the boric acid buffering does not contribute the the outgassing of carbon dioxide. This is very similar to CYA since that also does pH buffering (in addition to its primary role as a chlorine buffer) and also does not contribute to CO2 outgassing.

Gee, you guys really like throwing out numbers to explain, don't ya!
OK, here goes. We now know that the ppm number for borates is really a measurement of Boron which has a molecular weight of 10.8117 while the TA is measured as ppm CaCO3 which has a molecular weight of 100.0892 (but remember that CaCO3 is CO3(2-) for alkalinity which counts twice as much as a single charged species such as OH-).

Now the alkalinity from Sodium Borate comes from the following reaction:

B(OH)3 + H2O <--> B(OH)4(-) + H+ pKa is about 9.0

So -log( [B(OH)4(-)] ) + pH + log ( [B(OH)3] ) = 9.0
and at a pH much less than 9, say at 7.5 or so, most borate is in the form of B(OH)3 whereas the alkalinity comes from B(OH)4(-)

30 ppm Borate = 30 mg/l Borate
(30 mg/liter) / ( (1000 mg/g) * 10.8117 g/mole) = 2.775x10^(-3) moles/liter

log( [B(OH)4(-)] ) = pH + log(2.775x10^(-3)) - 9 = -4.06
so [B(OH)4(-)] = 10^(-4.06) moles/liter
technically I should subtract this from the 2.775x10(-3) number and iterate (or solve the equation directly which is what I usually do), but this is an error of only about 4% so I'll ignore it.

So, converting to ppm CaCO3:
(10^(-4.06) moles/liter) * (100.0892 g/mole) * (1000 mg/g) / (2 B/CO3) = 4.4 ppm CaCO3

Unless I did something wrong, it looks to me like they forgot the factor of 2 needed to convert from the alkalinity of single charged B(OH)4(-) to the "twice as much" alkalinity of double charged CO3(2-). Either that or they made a different assumption for pH such as 7.86 which would give me a result of 10. Or they are using an equilibrium constant pKa of 8.64 (that's more likely). As is the usual case, I found a variety of different equilibrium constants from different sources but finally chose the one that I thought was most accurate and also had a temperature dependence that I could derive and put into the spreadsheet.

I had already put the equilibrium equation and constants with temperature dependence into the spreadsheet -- I just didn't hook up all the exact calculations for the different species since that's a pain due to the interations for ionic strength that I have. I'll get to it...

Richard