Low pH but high TA and pH keeps dropping

[JaceTheAce]

Summary: Out of the tap my water has low-ish pH (7.2) and high TA (120). The TA has been stable but the pH keeps dropping. over the past 6 weeks I keep adding borax to raise pH but not affect TA and it works, but then after a week or two the pH drops again. I've scoured the TFP forums and Google and cannot find any answers so hopefully someone here can help me.

Details:

• 7300 gallon pool
• Chlorinated with Clorox 3" Trichlor tabs
• Pool is always covered overnight until ~2pm with a blue solar cover (bubble wrap type)
• The 2-speed 1.5 HP cartridge pump runs 24/7 at low speed and the pool is crystal clear
• Latest measurements as of yesterday (Aug 5, 2020):
  • FC = 5.0
  • pH = 7.1
  • TA = 120
  • CYA = 60
  • Temp = 92 F

The pool pH stayed stable at 7.2 from Mar - July then started to drop. Per the TFP app I added a box of Borax and it put the pH at 7.6. Then over 2 weeks it dropped and kept dropping to 7.1. I added another box of borax and again it was at 7.6 but over 2-3 weeks dropped back below 7.2. So yesterday I added another box of borax and pH is currently sitting at 7.4. I measure pH & Chlorine/Bromine daily using the Taylor K-100 and I measure the other levels weekly. TA, CYA, and CH all seem to stay steady. I live near SLC Utah so it's hot and dry in the summer and we don't get a lot of rain.

Questions:

• Is it normal for pH to drop but TA to remain the same?
• Is it OK to keep periodically adding Borax to raise pH? I know borates stay in the water.

 

[BowserB]

Your CYA is a little high. Check the table for Target free chlorine for 60 CYA (7-9ppm I think). If I'm not mistaken, the the Trichlor tabs also add acid to the water, besides increasing the CYA. You could try switching to liquid chlorine and see if that stops the pH drop without adding more borax.

 

[jseyfert3]

Is it normal for pH to drop but TA to remain the same?

No it's not. It's because you have a bad assumption that adding borox is TA neutral. This is not correct, adding borox increases TA.


Triclor tabs drop pH and lower TA. So basically you've been lowering pH and TA with trichlor and then re-adding TA and increasing pH with borax.

You should probably switch to liquid chlorine, your CYA is already high and trichlor won't work much longer (plus the Clorox brand adds metals like copper you don't want). Dropping the trichlor will mean your pH will stop dropping and should actually start increasing.

Is it OK to keep periodically adding Borax to raise pH? I know borates stay in the water.

No, you don't want too much. If you want to keep using trichlor you should probably switch to washing soda (sodium carbonate) to raise pH and TA to counter the effects of the trichlor acidity dropping both of them.

 

[Dan Morrill]

I made the switch from 3" trichlor to liquid chlorine this year after finding this forum. I had the same chemistry issues at the start of the season: high TA and low pH. It's a hard combo, because the high TA buffers pH changes and makes it hard to increase it, and the only way to lower TA is to add acid.....

The solution is as Bowser suggested: get off the trichlor tabs. They are the reason your pH is dropping, and will also cause you a headache really soon by raising your CYA too high.

 

[jseyfert3]

@JaceTheAce I see in your other thread you mention struggling with pH drop every week. Are you still having pH drop, and if so, are you still using trichlor tabs? If not, did you switch to liquid chlorine or what are you using now?

 

[JaceTheAce]

@JaceTheAce I see in your other thread you mention struggling with pH drop every week. Are you still having pH drop, and if so, are you still using trichlor tabs? If not, did you switch to liquid chlorine or what are you using now?

Yes, using Chlorox trichlor 3" tablets for convenience.

My borate levels started to reach the 60ppm range so I stopped adding borax and tried aerating. It worked. I aerated for 7 hours and was able to get the pH from 7.1 up to 7.3. I'm aerating for another 8 hours today. Details are here: My $5 Return Jet Aerator

 

[JaceTheAce]

I made the switch from 3" trichlor to liquid chlorine this year after finding this forum. I had the same chemistry issues at the start of the season: high TA and low pH. It's a hard combo, because the high TA buffers pH changes and makes it hard to increase it, and the only way to lower TA is to add acid.....

The solution is as Bowser suggested: get off the trichlor tabs. They are the reason your pH is dropping, and will also cause you a headache really soon by raising your CYA too high.

We had an Intex pool for years to the tabs are all I'm familiar with. Do you just use chlorine bleach? If not, what do you use and where to you get it from? How often do you typically add the liquid stuff?

FWIW, I've been keeping a close eye on the CYA and it's rising very slowly. I need to drain off about 8" to winterize the pool and when I reopen I was planning on draining of more making the equivalent of a ~50% drain + refill to address the CYA issue.

 

[jseyfert3]

Yes, using Chlorox trichlor 3" tablets for convenience.

My borate levels started to reach the 60ppm range so I stopped adding borax and tried aerating. It worked. I aerated for 7 hours and was able to get the pH from 7.1 up to 7.3. I'm aerating for another 8 hours today. Details are here: My $5 Return Jet Aerator

FWIW, I've been keeping a close eye on the CYA and it's rising very slowly. I need to drain off about 8" to winterize the pool and when I reopen I was planning on draining of more making the equivalent of a ~50% drain + refill to address the CYA issue.

Okay, perfect. I saw that other thread, that's why I asked. That aerator is stupid simple, which makes in insanely clever. I like it. But I posted here because I want to make sure you understand the chemistry behind things. There's nothing wrong with continuing to use trichlor tabs if you're monitoring CYA as you are and maintain the appropriate FC/CYA ratio. But, since you can't add any more Borax to replenish the pH and TA loss from the trichlor, note that you will start to see your TA drop. Just keep an eye on that. It it gets super low (below 50 ppm) you can add more TA with baking soda without adding any Borax.

Do you just use chlorine bleach? If not, what do you use and where to you get it from? How often do you typically add the liquid stuff?

I use "Pool Shock Liquid Chlorinator" from Menards. You don't have Menards in Utah but liquid chlorine is available at many home improvement stores and Walmart over the summer, or pool stores carry it. The name varies, usually referring to shock or liquid chlorine. The key thing is just check the ingredients and verify the only active ingredient is sodium hypochlorite. I use the Menard's stuff cause it's 12.5% for $3.99/gal. You can use unscented chlorine bleach, but only house brand stuff as all the Clorox now has splashless additives which you don't want, but it just typically costs a bit more than the higher concentration pool stuff once you do the math. I added every day or every other day in the peak of summer, but additions fell off a bit over time.

If you want more details on my additions, check out my logs. Just click my username, then click "Poolmath Logs". The spa is first and there's a lot of testing, my Intex pool starts about 2/3rds the way down, I recommend searching for "Intex" on that page to jump to those test logs rather than scrolling.

 

[JaceTheAce]

Okay, perfect. I saw that other thread, that's why I asked. That aerator is stupid simple, which makes in insanely clever. I like it. But I posted here because I want to make sure you understand the chemistry behind things. There's nothing wrong with continuing to use trichlor tabs if you're monitoring CYA as you are and maintain the appropriate FC/CYA ratio. But, since you can't add any more Borax to replenish the pH and TA loss from the trichlor, note that you will start to see your TA drop. Just keep an eye on that. It it gets super low (below 50 ppm) you can add more TA with baking soda without adding any Borax.



I use "Pool Shock Liquid Chlorinator" from Menards. You don't have Menards in Utah but liquid chlorine is available at many home improvement stores and Walmart over the summer, or pool stores carry it. The name varies, usually referring to shock or liquid chlorine. The key thing is just check the ingredients and verify the only active ingredient is sodium hypochlorite. I use the Menard's stuff cause it's 12.5% for $3.99/gal. You can use unscented chlorine bleach, but only house brand stuff as all the Clorox now has splashless additives which you don't want, but it just typically costs a bit more than the higher concentration pool stuff once you do the math. I added every day or every other day in the peak of summer, but additions fell off a bit over time.

If you want more details on my additions, check out my logs. Just click my username, then click "Poolmath Logs". The spa is first and there's a lot of testing, my Intex pool starts about 2/3rds the way down, I recommend searching for "Intex" on that page to jump to those test logs rather than scrolling.

Thanks for taking time to reply. I really appreciate the info!

 

[duraleigh]

Not only are the 3"tabs driving down your pH but they are adding constantly to your CYA which you do NOT want.

Convenient or not, you likely need to switch to LQ before your CYA runs away.

 

[JaceTheAce]

Not only are the 3"tabs driving down your pH but they are adding constantly to your CYA which you do NOT want.

Convenient or not, you likely need to switch to LQ before your CYA runs away.

Yeah, I see the problem. Thanks for the info. I've owned an Intex pool for several years and the pucks worked fine because it was small and we did a drain + refill every year. This year we installed a larger, more permanent AquaSport partially in-ground so now I'm getting educated on real pool maintenance. To close the loop here I did a partial drain + refill to get the CYA down and I'm now using liquid chlorine.

Thanks for all the help! The folks on this site are the best.