New Salt Water Pool - pH Craziness

[DB-Cooper]

See my signature for build info and build thread, but I built a ~27000'ish gallon SWG pool/spa. It's a gunite/plaster-pebble build. I'm religiously using the TF100 kit, the Taylor kits and a fairly expensive ($80) pH meter that's been routinely calibrated and matches well with the Taylor pH test.

I've got pretty much everything stabilized. I've been slowly and conservatively raising CYA, and my goal is to get to 65-70'ish, but here are my most recent results:

FC - 4-5
CC - 0-1 (5 drops no result, strips will show very low CC)
pH - let's discuss later
TA - 65-70
CH - 250-260
CYA - 40 (at present and slowly adding more)
Salt - 3500ppm
Temp - 82

Things are stable, and I have good control of things. I haven't added bleach in 2 weeks since I got the IC60 running. With the CYA slowly rising, I've been creeping the chlorinator down. I'm now down to 50% with 10.5 hours usage (5.25 hours of IC60). Granted, we've had some clouds recently, but even in 100% sunny days, I've been able to keep FC at 4-5.

Anyways, the one thing I can't rationalize or completely understand is my pH swings. I think I have a grip on how all this works, but I can't quite rationalize it, so let me explain how it's been going repeatedly for the last 2 weeks:

Focusing on CSI, I've been trying to keep pH at 7.8. Every morning, I test pH and I get 8.15-8.2. Pool Math will tell me to add ~20oz. of 31.45% acid to get down to 7.7, I oblige that request. I split the acid into two corners of the pool near two returns. Depending on how soon I test, I can see wildly different pH re-test results. Even 2 hours after, I can see numbers sometimes register in the high 6's (6.8). I don't test at the return, but it's not terribly too far away. 8 hours later, I will measure 7.5-7.6, and typically that's afternoon/evening swim time. My pumps turn off at 19:30, if I test then, I'll see 7.6-7.7. Testing again at 07:30, like clockwork it's back to 8.15-8.2. So despite the pumps, aeration and spillway all running during the day, it continues to climb after all pumps/features/swimmers are out to 8.15-8.2 by time I re-test in the morning. My spa will test at 8.5-8.6 in the morning showing a 0.5 pH higher average than my main body. The spa will test usually within 0.1 of my pool when I test after 8 hours of acid add and after running spillover.

While this is a new plaster pool (plaster poured in early April), I expected pH rise, but I'm trying to make sense of the overnight spikes and the spa going crazy high at rest. It's worth noting, my pool/spa is not well wind protected, the pool is above the trees, and I live in a canyon that gets above average wind, so I am probably getting topical aeration, but I get that in addition to pumps/spillways in the day as well. I also know for the first year, it's expected to be fighting pH, but I'm just trying to determine if any of this sounds strange. I think what throws me off is the high pH, subsequent adding of 20-25 oz of acid, then ultra low re-tests hours later, then high tests after night.

Long story short, I see no way to maintain any range other than to deal with these testing spikes. The only comforting fact is that it's consistent everyday in how it tests. I'm probably just testing too much and just dealing with daily spikes of half a pH and reading into it too much. Other anecdotal factors, It rained a lot last night, and it's the first time I haven't added pH in a 24 hr period in 2 weeks. pH tested 7.6 this evening, not adding since yesterday morning. We got 1-2" of rain, and rain is acidic, so it adds up.

I'm waiting for my PB to get out of here, but looking to add IntellipH. I travel a lot (when it's not Covid-19 lockdown), and adding daily acid doses is not something I could convince my wife to do.

Any input would be appreciated.

Cheers!

 

[ajw22]

Summary - You are testing pH too often. Lower your pH to 7.6 when it gets to 8.0. pH naturally rises over time in a body of water until it reaches a TA/PH equilibrium. That equilibrium is at a pH greater then 8. Any pH in the 7's is ok.

You can read TA - Further Reading

PH - Further Reading

www.troublefreepool.com

This table below summarizes the pH/TA equilibrium. This is further discussed in threads in the Deep End section.

Pool Water Chemistry

This thread presents my findings so far on pool water chemistry including the following: More Accurate Calcite Saturation Index (CSI) to replace Langelier Saturation Index (LSI) Calculation of ppm HOCl (disinfecting chlorine) at various levels of Total Free Chlorine (FC) and Cyanuric Acid (CYA)...

www.troublefreepool.com

 

[rmontgomery]

In addition to what ajw22 said, I just built my pool at the beginning of the year. It took about 3 months then all of the sudden the pH clicked into place. Really weird, but others have indicated the same. So just hang in there, it will eventually settle.

 

[DB-Cooper]

Thanks to both. I've been doing the 8.15->7.6 daily 24 ounce acid pour. It seems to be normal, but I do look forward to a future where it's a bit more stable.

 

[duraleigh]

Yeah, you are testing too much and asking for too much precision. As ajw22 said, anything in the 7's is essentially just fine.

Your other test results tell me the same thing......you are asking for too much precision again.

The CYA test is only good plus or minus 10 ppm (at best) and the TA test is good plus or minus 10 ppm as well.

The kits are designed to be perfectly adequate (and affordable) for TFP purposes but not to be laboratory precise.

After a heavy rain, I would probably allow pump run time of 2-3+ hours before testing.

 

[DB-Cooper]

Thanks, yeah it's easy to second guess the measurements, it's far from accurate. The ranges I provided were basically just capturing between 1-2 drops of accuracy.

I'm doing the full suite of testing once per week, and then testing chlorine and pH daily. I've not had to make a chlorine adjustment in 2 weeks, so I've got that dialed in. The pH is the only wild swing. All other levels are more or less stable week over week.

In regards to ajw22's comment about testing too often, I'm only testing pH daily. In my original post, I recorded additional information where I tested multiple times through the day. That was only done 1-2 times early on just to get an idea of how/when it was rising.

That said, I'm testing daily and basically seeing a 7.6 -> 8.15 daily increase. It's reliable but seems extreme, I'm just hoping it's the new pool thing. Earlier on in my pool opening, I was doing acid pours down to 7.0-7.2 and then it would take roughly two days to hit 8.x. I stopped doing that for two reasons:

1) The lower pH was putting my CSI into reportedly probelmatic areas
2) A friend told me pH will rise faster the lower it is, i.e. 7.0 -> 7.4 occurs faster than 7.4 -> 7.8 which occurs faster than 7.8 -> 8.2

So while I'm definitely over-thinking this, the pH has the largest impact on my CSI, and going down to low 7s puts my CSI at -0.90.

 

[duraleigh]

Tell me your latest (most current) pH, TA and CH

 

[jimbethesda]

If experts could also chime in on his spa return valve that he has partially open which results in a “mild” spillover while the pump is running in pool mode. How much, if any, would it help his PH rise if that valve was closed all the way and he just programmed a spillover once a day for 30-60 mins?

 

[DB-Cooper]

If experts could also chime in on his spa return valve that he has partially open which results in a “mild” spillover while the pump is running in pool mode. How much, if any, would it help his PH rise if that valve was closed all the way and he just programmed a spillover once a day for 30-60 mins?

I did test that. No difference between on and off. Similarly, no difference between bubblers barely bubbling and shut off. My spillover is barely a spillover. There’s no free fall, no splash, etc.

 

[DB-Cooper]

Tell me your latest (most current) pH, TA and CH

What I put in the post was as of yesterday morning accurate. TA and CH are very stable and haven’t moved within 10 ppm since weeks ago. pH is 8.15 in the morning, every day. I add 24oz to get me to 7.6-7.7 and it’s back to 8.15 the next day. It’s very reliable, my pH meter tests to 1/100th accuracy and it’s crazy how consistent the testing is. I test at the exact times every day, +/- 5 minutes.

 

[jimbethesda]

I did test that. No difference between on and off. Similarly, no difference between bubblers barely bubbling and shut off. My spillover is barely a spillover. There’s no free fall, no splash, etc.

Ok, good

 

[mgmoore7]

What I put in the post was as of yesterday morning accurate. TA and CH are very stable and haven’t moved within 10 ppm since weeks ago. pH is 8.15 in the morning, every day. I add 24oz to get me to 7.6-7.7 and it’s back to 8.15 the next day. It’s very reliable, my pH meter tests to 1/100th accuracy and it’s crazy how consistent the testing is. I test at the exact times every day, +/- 5 minutes.

When my pool was new, (about 10k gallons), I had to add 2-4 cups of acid daily to keep it in range. That lasted for to one degree or another for 6 months or so and then started to lessen. Now, my pool is 5 years old add acid a few times a week, maybe less. It is much more stable and I don't test it more than a week or so.