What makes TA go up? I only add acid to my pool.

[lovingHDTV]

I understand how to get rid of TA, I've read the great posts by Chem_Geek on the whole "soda pop" analogy, but what makes my pool TA increase?

I closed it at ~80ppm TA and opened it at ~140ppm. During the winter I continued to add acid to maintain a 7.6-7.8 PH.

I'm in the process of running the spa (great aeration) and keeping the PH beween 7.0 and 7.2 and the TA is now dropping. I seem to go from 7.0 - 7.2 PH in ~3 hours.

So back to my original question. What makes my TA go up? Maybe I can capture the process and sell it to "fix" flat soda

Not sure if it matters, but my pool is ~10 years old.

thanks,

 

[JasonLion]

It is unusual for TA to go up on it's own unless the pool is new. Sometimes blown in dust can increase TA, but that is rare. There are some chemical interactions with plaster that can raise the TA, but really only when the plaster is less than a year old.

 

[chem geek]

Normally, only the addition of TA in fill water (say, after evaporation) would make the TA rise or the explicit addition of something like baking soda (sodium bicarbonate) or washing soda (sodium carbonate). If you measured your CYA dropping over the winter, then the breakdown of CYA from soil bacteria (that found their way into the pool) could account for a rise in TA (but we'll see below). The breakdown of CYA is shown here and proceeds as follows:

CYA + 2H₂O --> Biuret + H⁺ + HCO₃^-
Biuret + H₂O --> Allophanate^- + NH₃ + H⁺
Allophanate^- + H⁺ + H₂O --> 2NH₃ + 2CO₂

so the net result is:

CYA + 4H₂O --> H⁺ + HCO₃^- + 3NH₃ + 2CO₂

The above degradation of Cyanuric Acid effectively adds carbonic acid as well as ammonia and carbon dioxide to the water both of which would lower the pH with no change in TA. If the carbon dioxide outgassed, the pH would rise with no change in TA.

So you have a mystery. Was there any other difference between the closing and opening numbers?

Richard

 

[lovingHDTV]

Here are my numbers:
15-Sep 22-Sep 7-Oct 14-Oct 27-Oct 25-Nov 19-Jan 6-Apr 9-Apr
F/C 5 5 4.5 6 2.5 2.5 6.5 1.5 12
CC 0 0 0 0 0 0 0 0 0
TC 5 5 4.5 6 2.5 2.5 6.5 1.5 12
pH 7.6 7.8 7.8 7.7 7.8 ~8.0 ~8.0 8.2+ 7.5
T/A 80 90 90 90 100 130 140 160 140
CH 600 - 650 650 650 - - 640 -
CYA 60 - 60 - - - - 55 -


Hopefully that is readable.

I do get a TON of leave and other organic matter in my pool in the fall and spring time. Could that be causing this? I've now added ~2 gallons of acid 1 quart at a time an have gotten my TA down to ~110 (this AM when I tested). I would like to not have to do this every year

thanks for you help,

 

[lovingHDTV]

Ok that is ugly, so I put it in the PDF.

thanks,

 

[chem geek]

Well, you've got me stumped. Maybe the leaves and other organic material have something or decompose into something that raises the TA, but that sounds pretty strange to me.

 

[lovingHDTV]

Oh, thats not good. Maybe that pool cover will help even more that just to keep the leaves out of the pool.

thanks,

 

[mas985]

Fill water is my problem. I would check yours to see if it is high in TA.

 

[chem geek]

During the summer, that would make sense, but I assumed that the pool was covered for the winter and that the water was unheated and cold which should have minimized it's evaporation. My own pool also rises in TA over time, but slowly, and some of this is due to evaporation and refill from the automatic fill line since the fill water has a TA of 80 and just gets added to the pool. However, I have a pool cover that is on most of the time so this minimizes this effect (but over a season, it's still measurable).

Richard

 

[lovingHDTV]

This did happen over the off season and I don't add water to the pool then, just rain water. I will check my fill water. I have checked it for CH, but not TA. My fill water comes from the houses water softner. Not sure it that makes a difference for TA, I know it does for CH.

thanks

 

[Guest]

Water softeners have no effect on TA.

 

[lovingHDTV]

My house water has a TA of 210.

Looks like I'll be constantly fighting my TA to keep it low enough to support my high CH.

I don't remember ever adding fill water during the winter, but I do at least know why my TA increases during the summer.

 

[chem geek]

I don't remember ever adding fill water during the winter, but I do at least know why my TA increases during the summer.

You might have a very slow leak. That would explain having more fill water introduced, even over the winter.

 

[mas985]

My house water has a TA of 210.

Looks like I'll be constantly fighting my TA to keep it low enough to support my high CH.

I don't remember ever adding fill water during the winter, but I do at least know why my TA increases during the summer.

I'm in a similar situation. I have very high TA, PH and CH fill water so by the end of the summer, the CH is well over 600 ppm. I refill every February since that is when the fill water is lower in CH (surface water).

The high TA fill water makes it nearly impossible for me to keep TA below 90 (except for the winter). So with a SWG, PH is constantly rising which led me to this solution. Now I fill the tank once every two weeks with acid and water which helps keep the PH below 7.7 so I don't worry too much about scaling.