Question on Total Alkalinity

[astrolite]

I read in "Pool School" under "recommended levels" that for vinyl pools the TA should be 70-90ppm, unless using Trichlor tablets for chlorine, then don't let it fall below 100ppm.

I am currently using Trichlor but am planning to switch to liquid chlorine, my TA is currently 70.

Why the different requirements?

 

[frustratedpoolmom]

TriChlor is acidic, lowers PH and the higher TA keeps the PH more stable, I believe. My TA is about 110, BBB for over one year. PH is steady.

Everyone's pool tends to experience slight differences due to weather conditions and various equipment. That's why you can see such wide ranges. If your pool has a source of aeration like a spa, waterfall feature, foutain, etc., lower TA's are recommended, because it helps keep the PH from drifting up due to the aeration.

 

[chem geek]

You can think of the higher TA as forcing a tendency for the pH to rise that helps offset the acidic Trichlor that tends to make the pH drop. If you use bleach or chlorinating liquid instead of Trichlor, then the higher TA could lead to a net pH rise while a lower TA would have the pH be more stable. It's counterintuitive because most people think of TA as buffering or stabilizing pH, but higher TA also causes the pH to rise more (or to drop less, when using Trichlor) by driving carbon dioxide out of the pool faster. This is why pools with more aeration features tend to rise in pH more (or drop less when using Trichlor) because they drive out carbon dioxide faster (think of a pool as being over-carbonated -- that's essentially what most of TA is).

Richard

 

[cscooper]

I'm also confused by total alkalinity, and whether it matters. Current numbers:
FC: 1.8
CC: 0.8
CYA: 20
pH: 7.2
TA: 260
CH: 170

This worked out to a 0.0 saturation index. tonight at a temp of 82F. I just converted from biguanide to BBB over the last week, and the conversion worked wonders on our cloudy green pool. :-D
Now the water is crystal clear, but the TA remains high. I've tried adding HCl but all that did was lower the pH without doing anything to the TA. I've made small attempts at aeration but once the pool cleared we kept it covered in order to heat it up getting ready for the 4th of July pool party.
Does this high TA really matter?

 

[JasonLion]

High TA doesn't matter unless it is causing a problem. The two common problems are constantly rising PH and high saturation index. In some cases, the PH doesn't rise constantly, but it jumps up dramatically when it rains. If none of those things are issues for you then you don't need to lower your TA.

 

[frustratedpoolmom]

I'm also confused by total alkalinity, and whether it matters. Current numbers:
FC: 1.8
CC: 0.8
CYA: 20
pH: 7.2
TA: 260
CH: 170

This worked out to a 0.0 saturation index. tonight at a temp of 82F. I just converted from biguanide to BBB over the last week, and the conversion worked wonders on our cloudy green pool. :-D
Now the water is crystal clear, but the TA remains high. I've tried adding HCl but all that did was lower the pH without doing anything to the TA. I've made small attempts at aeration but once the pool cleared we kept it covered in order to heat it up getting ready for the 4th of July pool party.
Does this high TA really matter?

Just want to chime in on your numbers....if your CC is really .8 you may want to shock again, any CC's above .5 and you should shock. Some pools develop CC's if kept covered. You may still have biguanide residue in your cover, or even in your filter medium, have you changed it since you completed the conversion?

Muratic Acid is better for lowering TA. Simple aeration won't lower TA, it will raise PH. You have to use Muratic Acid to lower TA and PH and then aerate to raise the PH back into range. You have to repeat this process several times to get the numbers to the recommended levels.

 

[cscooper]

Thanks. That was the next question I was going to post this a.m: when do you decide to shock? When the combined chloride is above a certain level? Would that be 0.5 ppm?
And then the next question: After you shock, when is it okay to go in the pool?
I did use muriatic acid. I just typed HCl because it has fewer letters to type. They're the same thing.
We are going to replace the sand in the filter today.
Thanks for all the help!

 

[frustratedpoolmom]

Thanks. That was the next question I was going to post this a.m: when do you decide to shock? When the combined chloride is above a certain level? Would that be 0.5 ppm?
And then the next question: After you shock, when is it okay to go in the pool?
I did use muriatic acid. I just typed HCl because it has fewer letters to type. They're the same thing.
We are going to replace the sand in the filter today.
Thanks for all the help!

How about MA I'm still learning all the different chems myself. Didn't know they were the same.

Yes, anything above .5 you should shock. Or if you are using a solar cover, and your at .5, just leave the cover off and the sun will usually destroy the cc's.

Shocking and swimming....it depends. The higher the CYA the higher your FC and its still okay to swim. I'd say around 10 ppm and wear an old suit....