Raising TA in the presence of a pH controller

[kouroubel]

The TA in my pool (180 m3) has dropped to about 60 ppm and I thought I should raise it to around 80 ppm by adding 5-6 kg of sodium bicarbonate.

Is there a reason I should turn off the automatic pH adjuster while raising TA?

 

[kimkats]

I would turn it off while you are doing an adjustment so you know exactly what is being done and how your pool responds. I think it will make it easier in the long run.

How are you testing the water?

Kim

 

[kouroubel]

I use the ColorQ Pro7 photometer...

 

[bdavis466]

Is there a particular reason you want to raise the TA? There is no reason for your pH adjuster to be effected if you did, but hold off until we get more info.

Can you post up the rest of your test results?

 

[pooldv]

Agreed, TA at 60 is fine if your PH is stable. Likely the reason it has dropped is due to acid additions to lower PH which has slowly lowered your TA over time.

 

[Patrick_B]

It has dropped from acid additions. No need to raise it if other parameters are in line, and your pH is stable. What is your Calcium level?

 

[kouroubel]

Is there a particular reason you want to raise the TA? There is no reason for your pH adjuster to be effected if you did, but hold off until we get more info.

Can you post up the rest of your test results?

Here are my test results:

CYA: 55 ppm, FC: auto-adjusted by ORP controller at 1 ppm (used to be at 3 ppm but lowered the setting for the winter), pH: auto-adjusted at 7.4, TA: 60 ppm, CH: 670 ppm (I know it is too high but what can you do?)

Chlorination is done with liquid chlorine (used to be trichlor but I changed it as CYA went to heaven after 3 months of operation).

The reason I want to raise TA is to be in agreement with the recommended values (80-100) suggested almost everywhere (including in this publication).

 

[bdavis466]

Your FC level is low for your CYA. With a level of 55, your minimum is around 4.

Maintaining a pH of 7.4 is a little on the low side. With your TA of 60 (leave that be), and let your pH rise to the 7.6-7.8 range.

Water replacement is the only way to reduce calcium levels. Although your level is higher than what is recommended, with careful monitoring you can compensate for it and be just fine. The CSI number in PoolMath will indicate when scale formation may become an issue and you can adjust your target numbers accordingly.

A higher pH with a low TA will significantly reduce your acid consumption.

 

[kouroubel]

As I said above, the FC level is low on purpose because it is winter and the pool is not used.

Now, regarding the calcium levels I believe that they are high because of the tap water used to fill the pool (I should do a measurement to verify that). What else would explain such a high CH value?

So basically what you are advising is that my TA level is fine and I should ignore the recommendations for 80-100, is that right?

 

[JamesW]

A ph of 7.4 and a ta of 80 to 100 creates too much carbon dioxide and is not stable. A ph of 7.7 to 7.8 and a ta of 60 is stable.

 

[bdavis466]

Every gallon of water that evaporates leaves its calcium behind since calcium does not evaporate. The water used to replace what has evaporated has calcium in it so the calcium level of your pool rises every time it is refilled.

 

[kouroubel]

A ph of 7.4 and a ta of 80 to 100 creates too much carbon dioxide and is not stable.

Do you know any links that explain this in detail? If there is a scientific explanation, I am more than interested!!!

A ph of 7.7 to 7.8 and a ta of 60 is stable.

But, isn't a pH value of 7.4 better than a 7.7 because of the increased HOCl percentage? Or maybe the difference is negligible because of the presence of CYA?

Every gallon of water that evaporates leaves its calcium behind since calcium does not evaporate. The water used to replace what has evaporated has calcium in it so the calcium level of your pool rises every time it is refilled.

I think you mean to say that calcium rises because of water evaporation and drops with water refill....

 

[Jezza]

Kouroubel- I think the two links that were posted on your other thread in 'Deep End' will provide you the explanations for your question above about TA, pH and CO2 outgassing and your question about pH increase when adding bleach or using a SWG.

In relation to your point about CH, I think the assumption is that your fill water could be high enough in CH to contribute to your high CH reading assuming that no products containing calcium have been added.

 

[kouroubel]

Thanks for pointing out. I should have looked a little bit past the answer to my question in the Deep End section.

 

[Leebo]

Is this pool a plaster, fiberglass or vinyl pool?? Adding this info to your signature will help in the future.

 

[kouroubel]

It is coated with ceramic pool tiles....

 

[bdavis466]

Do you know any links that explain this in detail? If there is a scientific explanation, I am more than interested!!!

See THIS post. A higher pH with a lower TA is much closer to being at equilibrium with the CO2 content of the atmosphere, thus pH rises much slower due to less carbon dioxide out gassing (the major contributer to pH rise).

But, isn't a pH value of 7.4 better than a 7.7 because of the increased HOCl percentage? Or maybe the difference is negligible because of the presence of CYA?

While this is true, the use of CYA reduces this down to a minuscule and somewhat undetectable level due to the lower precision of our water testing. Most find that slower pH rise and less acid use far outweigh a small loss in efficiency of HOCl that can easily compensated by running slightly higher levels and nearly eliminates a difference when using CYA. See THIS and THIS thread. There are many others like it.

I think you mean to say that calcium rises because of water evaporation and drops with water refill....

Refilling evaporate adds additional calcium to the water since the calcium did not leave with what evaporated. Even though the fill water is at a lower concentration that the pool water and the overall concentration is diluted, the calcium level still rises. An example: a pool's CH is 500 and 1000 gallons evaporate. The concentration is now higher (say 525) due to less dilution. We now refill the pool with a fill water that contains 150 ppm CH. Although the concentration is lower, and the now 525 ppm is diluted, you are still adding more calcium and the new CH level is 505ppm. CH slowly rises with time unless you get significant enough rainfall to overflow the pool or you pump water out and replace it.

 

[kouroubel]

Refilling evaporate adds additional calcium to the water since the calcium did not leave with what evaporated. Even though the fill water is at a lower concentration that the pool water and the overall concentration is diluted, the calcium level still rises. An example: a pool's CH is 500 and 1000 gallons evaporate. The concentration is now higher (say 525) due to less dilution. We now refill the pool with a fill water that contains 150 ppm CH. Although the concentration is lower, and the now 525 ppm is diluted, you are still adding more calcium and the new CH level is 505ppm. CH slowly rises with time unless you get significant enough rainfall to overflow the pool or you pump water out and replace it.

We are basically saying the same thing then.

Thank you for all the links!!!!