Raised Alkalinity now I can't drop my PH below 7.8?

[Vaggeto]

Hi all,

I've added 72 ounces of Muriatic acid over the last 3 nights into my 23.5K gallon gunite pool, but somehow my PH hasn't dropped!

I've recently had a slightly low alkalinity around 30ppm. I've always been able to add 31.45% muriatic acid at the indicated amounts on the PoolMath app, and it would drop PH accurately, but just recently I added baking soda to up my alkalinity to around 90-100ppm and boric acid to bring my borates to about 10ppm (all I had left) and since then the muriatic acid is no longer dropping my PH. I added 24 ounces each night over the last 3 to lower it from about 7.8 to 7.5 but when I test the next night it's been the same or even higher! I know Alkalinity acts as a PH buffer from PH lowering, but this seems far more drastic than I expected!

The pool was replastered in July 2023 which initially did cause PH to raise consistently, but the PH has been quite stable for most of this year.

To be more exact, last night it was 7.91 and I added 24 ounces and now about 7 hours later after the filter ran most of that time, it's only at 7.75. Can the muriatic acid somehow become ineffective? It didn't seem any less potent than normal and I finished one bottle and started another last night.

Any advice on what I should do? I was hoping to move to SWG within the next week, but wanted to get my Alkalinity and borates to be higher to keep the PH more stable.

Kind regards!

 

[ajw22]

The borates you have added are keeping your pH from lowering.

You tackled this in the wrong sequence. You needed to get your TA about 60 and pH in the mid-7's and stable BEFORE you add borates.

It will take larger doses of acid to lower your pH now with the borates in the pool.

Borates in pool - Further Reading

www.troublefreepool.com

 

[pjt]

I've recently had a slightly low alkalinity around 30ppm.

What test kit do you have?

How are you chlorinating?

Fill out your signature when you have a minute.

I added baking soda to up my alkalinity to around 90-100ppm

A non-trichlor pool should (almost) never need baking soda.

but wanted to get my Alkalinity and borates to be higher to keep the PH more stable

Lower TA slows pH rise. For a LC or SWCG pool, TA ~60 will result in a stable pH in the high 7s. TA of 50 or above is fine. It's the least important parameter and typically manages itself as you dose MA for pH control. What's the TA and CH of your fill water?

Borates are optional and should be considered only after you have everything else under control.

 

[Vaggeto]

Thanks for the advice and input!

Will fill out my signature. I have a TF100 test kit. (I recently added the salt portion as well and have the insta borate strips)

I use mostly liquid chlorine (Walmart Pool Essentials 10%) and occasionally di-chlor 1lb bags (costco had a great sale and it adds a bit of CH which I need to raise some). I also use tri-chlor mostly when out of town, but also just to generally add a bit of chlorine and to add a bit of CA.

I'm currently at a PH of 7.71
1.5ppm chlorine (tested just now at end of day)
~15 CA (I typically keep this around 30, but due to some drain and refilling and a recent accidental overfill, it's low. I plan to go to SWG soon and keep 70-80 CA)
TA ~80ppm (just tested tonight)
CH 210ppm
Borate 10ppm
Salt 900ppm
Temp 85*

I plan to bump CH up to around 350 but was holding off in case it should be slightly lower moving to a SWG.

My TA was around 20-30 for quite awhile before I recently added the baking soda.

I thought TA buffered PH from lowering, and Borates buffered PH from rising? So I'm surprised to hear the borates might be the biggest culprit of my PH staying high when adding MA.

My fill water CH is 150. I don't think I've added any baking soda since last fall. I just tested my tap TA and I'm shocked to say it tested at 100ppm. I don't know how it could have been so low prior after some refilling and overfilling, except for the fact that all of this past fall I had to use a lot of MA to keep the PH down due to what I believe was the plaster curing process.

 

[pjt]

di-chlor 1lb bags (costco had a great sale and it adds a bit of CH which I need to raise some)

Dichlor doesn't affect CH.

I also use tri-chlor mostly when out of town, but also just to generally add a bit of chlorine and to add a bit of CA.

Use the term "CYA". CA is easy to confuse with calcium.

I'm currently at a PH of 7.71

How are you getting that reading? The TF-100 doesn't have that kind of precision.

1.5ppm chlorine (tested just now at end of day)
~15 CA

That isn't enough FC or CYA. For the DFW area, I'd suggest a CYA of 50-60 (and corresponding higher FC) until you get your SWCG online. Pass a OCLT before bumping up your CYA.

I plan to bump CH up to around 350

I would only add a small amount of calcium, enough to achieve 250. With fill water CH of 150, your CH will climb with evaporation and fill water top ups.

My TA was around 20-30 for quite awhile before I recently added the baking soda.

Are you continuing to add drops until there's no further color change? Do you use a SpeedStir?

I just tested my tap TA and I'm shocked to say it tested at 100ppm.

Every time you add fill water, you're increasing your TA. (Same effect as adding baking soda.)

I don't know how it could have been so low

Excessive MA and lots of rainfall (which has a TA of essentially zero). When your TA is 50-70, you need to be judicious with MA dosing. Only add enough to get the pH into the high 7s.

 

[Vaggeto]

Dichlor doesn't affect CH.


Use the term "CYA". CA is easy to confuse with calcium.


How are you getting that reading? The TF-100 doesn't have that kind of precision.


That isn't enough FC or CYA. For the DFW area, I'd suggest a CYA of 50-60 (and corresponding higher FC) until you get your SWCG online. Pass a OCLT before bumping up your CYA.


I would only add a small amount of calcium, enough to achieve 250. With fill water CH of 150, your CH will climb with evaporation and fill water top ups.


Are you continuing to add drops until there's no further color change? Do you use a SpeedStir?


Every time you add fill water, you're increasing your TA. (Same effect as adding baking soda.)


Excessive MA and lots of rainfall (which has a TA of essentially zero). When your TA is 50-70, you need to be judicious with MA dosing. Only add enough to get the pH into the high 7s.

Oops, sorry I was mixing up dichlor with Cal-hypo. The 1lb bags are cal-hypo.

Ahh gothca, CYA. Thanks!

I'm testing with an calibrated electronic multi-sensor that I got to initially get an idea of my salt and quick PH readings. When I test it I also still test with the TF-100.

Just to clarify, I had 1.5PPM FC after the entire day of sun and use. I then added 4PPM liquid chlorine, which would again slowly drop throughout the next day due to low CYA.

Historically, I keep my FC about at about ~3ppm, CYA at 30, and PH around 7.5, bumping it down to about 7.3 when it gets up to 7.8 or so. I've never had anything but a sparkling clear pool with this process, unless I forget to add any chlorine for multiple days. I like to keep the chlorine on the lower end due to a preference for some who are more sensitive to it. And keeping a lower CYA allows the FC to be more effective at a lower ppm, although I know this results in more cost due to lost chlorine to the sun. I go a bit higher than the 3ppm FC at night (4-5), knowing it will drop in the day and we usually swim after 5pm or so when chlorine level is lower.

As I plan to go to SWG, I've been reading that 80ppm CYA is ideal for the most efficient SWG need, but that does require keeping a constant higher FC of like 8-10ppm or so? I'm still not sure I will go that high, as I may prefer to run my SWG a bit harder and keep both CYA and FC on the middle or lower end. Although I'm not 100% clear on the relationship of a higher FC ppm and a higher CYA and how that could impact those sensitive to chlorine. I know the FC is less "available" but I'm not sure on the actual sensitivity and if it's raw FC vs "non-bound" FC.

Ahh thanks for the input on the CH. I didn't consider it naturally going up due to evaporation and refilling. I've had some slow leaking issues in the past so I think that has offset this natural rise in most things.

For TA, I use a speed-stir and 10/25mL sample sizer and I typically waiting until it changes to a brighter color, and then add a couple drops after to see if it changes much. So for example if it's 85 TA, typically I will see it change colors and revert back quickly for drops 5-6, drop 7 might start the permanent change but a weak color, drop 8 will be more "bright" and then I will do a drop 9 and 10. The 9th to see if get's much brighter which it might just a bit and the 10th to verify it doesn't change at all. Then I will assume it's basically between between drops 8-9 or around 85.

Yes I never considered that would increase my TA. It's always been rather low, so I really assumed fill water only had around 30ppm or so and that was where it would naturally revert until I added more baking soda, but now I see it's likely just balancing there naturally due to me keeping my PH around 7.5 and the MA offsetting the baking soda over time?

Honestly, my PH almost never drops on it's own and only goes up, so I outside of the plaster needing it, I don't really see any value in intentionally keeping a higher TA. I was honestly just trying to bring it up as part of pre-balancing the pool fully before adding the SWG. Sadly it seems I should have started with a lower PH if I was going to add any baking soda, and really just not put so much only to go up to around 50ppm or so.

When I see PH of 7.7 and above, all i can think of is the pool being out of balance with our natural PH, and the FC being less effective the higher the PH. So mentally it's hard for me to accept a 7.8-7.9PH. But I guess until my TA goes down over time with using MA, I'll learn to accept the high 7s.

Thanks again for all of the input and advice!