Can't seem to get TA below 100

[azkevman]

First off, a huge thanks to everyone here at TFP...your knowledge has been indispensable. So, I am going on 3 weeks now of BBB. I did a 80% drain and refill 3 weeks ago to resolve a high CYA issue. Here are what my numbers were immediately after refill:

FC: 5.5
CC: 0.5
pH: 7.6
TA: 130
CH: 140
CYA: 50 (slightly less, but I will use this as my number)

Since then I have been mostly focused on FC and pH to get to know how they will act. Due to the heat and amount of sun here in AZ, my pool consumes allot of FC each day. On average over the last 3 weeks I have had to dose about 110oz. of 10% each day. Its cooling off a bit so I am seeing the consumption come down a bit. I see pH rise about 0.2ppm per day, which means I am adding acid to lower back down to 7.2 about every 4 days. Finally today I added 15lb of Calcium Chloride to increase the low CH (fill water passes through a water softener). Here are my numbers as of today:

FC: 7
CC: 0
pH: 7.7
TA: 100
CH: 260
CYA: 50

My big question is related to the TA. I would have expected that it would have come down below 100 by now. Over the past few weeks I have added 239oz. of 14.5%, and 106oz. of 34.6% acid, which according to PoolCalculator combined should have lowered my TA by a total of approximately 53ppm (the calculator at the bottom does not contain those specific % to choose from), however other than the initial drop down to 110, I consistently get reading of 100-110ppm.
Does TA rise, and is it rising faster than I can keep up with it, or is there something else I should be doing? I would like to get it down to the 70-80 range to try to get my pH to stabilize more.

Your thoughts are greatly appreciated.

edit: oh and my water looks great! Never knew it could look so clear and sparkling.

 

[chiefwej]

When you add acid to lower pH it does lower TA. Your problem is that as the pH rises again so does your TA. The way to lower TA is to bring the pH down around 7.1 or 7.2, then use aeration which will cause the pH to rise without raising the TA. You have to repeat that process over and over, until the goal TA is reached.


READ THIS:
http://www.troublefreepool.com/pool-school/lowering total alkalinity

 

[azkevman]

OK, so that's what I wasn't clear on...that TA naturally rises as pH rises. So rather than using acid every time I hit a pH of 8 every few days, it looks like maybe I should add a little acid every day and also aerate...and that should lower TA faster...am I understanding that correctly?

Sent from my mobile device using Tapatalk 2

 

[Bluegrassman]

OK, so that's what I wasn't clear on...that TA naturally rises as pH rises. So rather than using acid every time I hit a pH of 8 every few days, it looks like maybe I should add a little acid every day and also aerate...and that should lower TA faster...am I understanding that correctly?

Sent from my mobile device using Tapatalk 2

That is my understanding as well. By following this method, you are lowering your pH and TA at the same time, then raising pH back up with aeration, which does not affect TA. Continue this until you reach your target. I use my waterfall for aeration, but I've seen many post on here about pointing the return eyeballs up toward the surface to create bubbling/aeration that way.

 

[chiefwej]

Click on the link. It's all explained in the article.

http://www.troublefreepool.com/pool-school/lowering total alkalinity

 

[azkevman]

Click on the link. It's all explained in the article.

http://www.troublefreepool.com/pool-school/lowering total alkalinity

Right, thanks. That is where I got the smaller more frequent dosing of acid, as long as I understand it correctly.

Sent from my mobile device using Tapatalk 2

 

[azkevman]

I have been doing infrequent aeration with a wall fountain that covers most the pool when on. I will run it more often as I dose acid more often.

Sent from my mobile device using Tapatalk 2

 

[UnderWaterVanya]

I think some misunderstanding is creeping in. You say you have lowered pH using MA and pH is rising by 0.2 per day. Just to be clear you are not adding anything to make pH rise correct?

Essentially you are already performing the steps to lower TA. The aeration only speeds the process. If you have pool volume and other chemistry set correctly in the pool calculator then the MA's impact should be on pH and TA as predicted. If you are seeing TA staying unchanged but pH falling as expected it is not the MA being weaker than expected that is causing the problem.

I'm stumped

 

[azkevman]

I think some misunderstanding is creeping in. You say you have lowered pH using MA and pH is rising by 0.2 per day. Just to be clear you are not adding anything to make pH rise correct?

I have been adding acid every time the pH hits 8, to bring it down to between 7.0-7.2, then from there it rises .20 each day, and I repeat when it hits 8 again.

Other than the Calcium Chloride I added today to raise CH, I have only added bleach and acid over the last 3 weeks.

Sent from my mobile device using Tapatalk2

 

[azkevman]

Just had a thought...how does evaporation affect TA? I read an article here in Phoenix recently that said the average pool in Phoenix loses 2,500gal per month to evaporation. That would mean 15% of my water evaporates monthly!
My fill water has a TA of 130, so if I'm replacing the 15% evaporated with a higher TA fill, then it may be countering my attempts to lower it with acid...
Does that seem likely?

Sent from my mobile device using Tapatalk2

 

[chem geek]

Evaporation and refill increases TA because whatever is in the tap water gets added to the pool. So water with 100 ppm TA that has 15% evaporation and refill with 130 ppm TA water ends up with 100 ppm * 0.85 + 130 * .15 = 104.5 ppm so while it increases, it's somewhat slow though would be noticeable over multiple months.

As for lowering the TA more quickly, you want to add acid more frequently to keep the pH lower (7.0 to 7.2) since low pH outgasses faster. And of course the aeration helps as well. All the TA lowering procedure does is to accelerate a process that would occur anyway if you just added acid to maintain pH over time. The total amount of acid that needs to be added to lower the TA is the same in both situations, but by lowering the TA more quickly one can have the pH rise more slowly.

 

[UnderWaterVanya]

I think you nailed it - the higher TA in your fill water is likely why you've seen a plateau in your attempts to lower TA. increased aeration will (as mentioned by others) increase the rise in pH allowing you to use more acid and lowering the TA more quickly.

However given your fill water and evaporation rates it may be a never ending battle.

 

[azkevman]

OK, makes sense. So the rise in TA due to evap/refill looks like it would be at a slow enough rate per month that It shouldn't be significantly hard to stay on top of once I get it down to where it should be.

I am going to keep pH down daily to 7.2, rather than letting it rise to 8.0 before dosing with acid, over the next week and see what happens.

Thanks everyone!

Sent from my mobile device using Tapatalk2

 

[ping]

I calculated that you are using about 6 ppm of chlorine a day. Have you run an OCLT since you drained your pool. If you were having problems holding chlorine before you drained, you might still have a slight problem with it. There can still be algae if you did not go through the full shock process after you changed out the water. The amount of chlorine you are adding is keeping the algae from blooming but it might not have killed it all. Your pool can still look clear, have <.5 CC, but not pass the OCLT.

I suggest raising the chlorine up to the high end of your target one night and run the OCLT to rule out any organics in the water. You are boarder line on your chlorine consumption but definitely on the high side. If your pool has a lot of use then that much consumption could very well be normal.

 

[azkevman]

Yeah, I have ran 2 OCLT's since refill and both passed with 0ppm loss. So I have confirmed my FC loss is only occurring during the day. The pool is typically used daily, and gets direct sun for about 10 hours or so. We had a week of 115°+ temps shortly after the drain and refill, which drove the water temp up to 94°…so I'm sure that contributed greatly to my FC consumption.

Sent from my mobile device using Tapatalk2

 

[UnderWaterVanya]

Yeah, I have ran 2 OCLT's since refill and both passed with 0ppm loss. So I have confirmed my FC loss is only occurring during the day. The pool is typically used daily, and gets direct sun for about 10 hours or so. We had a week of 115°+ temps shortly after the drain and refill, which drove the water temp up to 94°…so I'm sure that contributed greatly to my FC consumption.

I have a CYA of 55 or so and only get sun from 10am - 5pm and the temps have been below 90 almost every day this month. I see a daily use of 3-4ppm myself. I have passed all the OCLT's I have run - some with 1ppm loss, some with 0ppm loss etc.

7ppm seems high but you have a lot more sun than I do.