Should I raise my TA now?

[halefmly]

Back in September I aerated and successfully lowered my TA to 80 in response to some useful guidance in this forum. I still test weekly, and am now wondering if I should be concerned that my TA is getting too low.

Here are my results from this morning:
FC 3.5
CC 0
TC 3.5
pH 7.5
Alk 70
Cal 450
Cya 45 (this has lowered from 60 back in the summer)
Temp 49
Salt 3200

Typical results from the fall:
FC 8.0
CC 0
TC 8.0
pH 7.6
Alk 80-90
Cal 470
Cya 60
temp 69
salt 3200

[chem geek]

Normally, colder water has a higher pH naturally (i.e. cooling pool water without doing anything else to it will raise the pH by about 0.2 going from 85F to 50F) but your lowering of TA and targetting a pH of 7.5 has made your water slightly corrosive, but nothing to worry about (index is -0.3) especially in cold temps where reactions are slow. So relax and just let the pH drift up naturally if it wants to do that, but if it doesn't, that's fine too.

Though I target around 7.5 for my pool in the summer, it natrually drifts to 7.7 in the winter as the temperature cools down. Then when the water warms up again, it naturally comes back down to 7.5.

Richard

[halefmly]

Richard,
Thanks for the reply. I have been adding acid about every two or three weeks whenever the pH got up to 7.8, but I'll relax while the water is cold, and let the pH rise.

On a related note, after reading "The Great Tetraborate Experiment" thread, I ordered some borate test strips, and plan to add borax up to 50ppm. It seems that you and some of the other advanced chemists in this forum are using some more advanced equations with the test results posted by us beginners. Based on the water chemistry I have posted here, what should I do regarding adding borax? I understand that I will have to add even more acid to counter the pH rise caused by the borax, but I don't want to cause great swings in the pH. Is it possible to add borax and acid in the correct proportions to maintain a good pH balance?

[chem geek]

Larry,

Every pound (which is about a cup) of 20 Mule Team Borax requires about 7.7 ounces of Muriatic Acid (31.45% HCl) to keep the pH the same so you can add one and then the other in smaller quantities to keep the pH more stable (you don't mix them together, of course, you just put them into the pool one after the other).

For your size pool it would take 1219 ounces or about 76.2 pounds of 20 Mule Team Borax which is about 16 boxes. It would take about 582 ounces of Muriatic acid to keep the pH the same after adding the Borax. Of course, you should add about half of each of these amount (alternating in smaller additions of each) and then measure your Borates level on the test strip just to be sure you don't go to far and that my calculations were correct.

Richard

[giroup01]

What is the BleachCalc using as borax concentration, or maybe I should be asking if the borax concentration in BleachCalc is the same as the 20 Mule product, the software says 338 ounces in 20700 gallons gets you 49.9 ppm. Just wondering.

And many thanks Richard for your last reply on my high TA/pH drift question!!

[chem geek]

Evan (waterbear) and I figured out what the proper interpretation of "ppm Borates" means and it turns out to be ppm of Boron, not tetraborate or boric acid or anything else. BleachCalc was not using that convention so would produce the wrong result. I believe there is more about this in The Great Tetraborate Experiment (http://www.poolforum.com/pf2/showthread.php?t=4712) thread.

Richard