pH and alkalinity question

[Hchang]

I have a 17,500 gallon Gunite chlorine pool that was finished in October of 2020 (Central Texas). It has an attached spa with overflow waterfall and a heater. I’ve been using the TFT-100 to test and manage chemicals myself for the past couple of months. I have the pH probe (calibrated) that came with my kit, but it never reads below 7.9, even when the reagent test does. So I don’t trust it completely. I have a new Apera one coming this week

I’ve read a lot of information about pH and alkalinity but am looking for advice here. I notice my pH is constantly drifting to 8.2-8.3. Even when I use Pool Math to dose the muriatic acid to get to 7.6, it almost never reaches that and will bounce back up within 48 hours.

Pool math says my alkalinity is “recommended” to be 50-90 and “ideal” is 60-80. So I’m in that range. In fact, my TA read 60 yesterday for the first time (I’m sure it’s from the every other day acid dosing I’m having to do). usually it’s been reading 70-80.

Advice on how to handle such constant pH swings? Is there something I am not attending to here?
Latest readings attached.

 

[cowboycasey]

get your FC up now so you do not have a bloom and have to start slamming..

Drop your PH to 7.2 and it will take longer to get to 7.8 then drop it again.. Your TA is great at 60...

Are you running your waterfall everyday all day.. your PH will raise fast and your not going to stop it until you stop using the waterfall so much.. can you run it an hour in the morning and an hour at night?

 

[Hchang]

Updated with signature.

 

[Hchang]

get your FC up now so you do not have a bloom and have to start slamming..

Drop your PH to 7.2 and it will take longer to get to 7.8 then drop it again.. Your TA is great at 60...

Are you running your waterfall everyday all day.. your PH will raise fast and your not going to stop it until you stop using the waterfall so much.. can you run it an hour in the morning and an hour at night?

Thanks for the reply. Yes I added liquid chlorine right after this reading.

Yes we run the VS pump 24-7. When our pump is running, the waterfall runs. The only way to turn off my waterfall is to put it on spa mode. For most of the day the pool pump is running on low (1850 rpm) and the waterfall from the spa is just a low trickle. But I am sure that it still is contributing to pH rise. For two hours in the morning and four hours in the afternoon, the pump is set to run on high (3150 rpm). The pool company set it up this way and I added the two hours in the morning just last week because we have been having a huge pollen bloom in Austin and it helped with surface skimming. Advice? Maybe I should cut back on the hours in high mode?

I guess one problem I’m having is even getting the pH to budge. Or at least to reach my target. Yesterday when it read 8.2, I dosed the acid to reach 7.4 (per pool math recommended amount) and this morning it was reading 7.8. So I feel like I have to really OVER dose to get it close to a target. I’ll take your advice and shoot for even lower and then redose when it creeps to 7.8.

 

[cowboycasey]

You are not running at low speed, you are running over my fast speed... Low speed is 800 to 1000 RPM.. I run my SWG at 1600 for 2 hours and that is the highest speed I run mine.. Then I run from 8 am to 8pm on 800 RPM, That is why we bought these VS pumps to run them low.. The pool company set them up that way because they normally deal with 1 speed pumps and that is all they knew...

Try running at 800 to 1000 rpm for most of the time and run at 1800 for those couple hours you want it higher...

 

[proavia]

How did you get a CYA of48?

What is the TA, pH and CH of your fill/tap water?

Show us a few pics of your equipment pad and plumbing setup.

 

[mknauss]

Welcome to the forum!
What automation system do you have to operate your spa?
I suggest you read ABC's of Pool Water Chemistry.

 

[Hchang]

You are not running at low speed, you are running over my fast speed... Low speed is 800 to 1000 RPM.. I run my SWG at 1600 for 2 hours and that is the highest speed I run mine.. Then I run from 8 am to 8pm on 800 RPM, That is why we bought these VS pumps to run them low.. The pool company set them up that way because they normally deal with 1 speed pumps and that is all they knew...

Try running at 800 to 1000 rpm for most of the time and run at 1800 for those couple hours you want it higher...

Ok! Thanks for this recommendation! I will try that!

 

[Hchang]

How did you get a CYA of48?

What is the TA, pH and CH of your fill/tap water?

Show us a few pics of your equipment pad and plumbing setup.

CYA of 48 was admittedly an estimate on the cylinder that came with my TFT-100. It was reading between 45-50.
I don’t know the readings of my fill water, that’s a good idea to test. thank you.

I can add pictures of equipment when I’m home tomorrow.
thank you!

 

[Hchang]

Welcome to the forum!
What automation system do you have to operate your spa?
I suggest you read ABC's of Pool Water Chemistry.

Hi! And thanks for the replying!
I’m not exactly sure what automation system you mean for the spa. The entire pool and spa are controlled through Pentair ScreenLogic panel and app. That is how we turn on the spa, heater and control the pump. Is that what you are asking?
And thanks for the link to the Water Chemistry, I’ve read that a few times already. I know I have things contributing to my pH (like my water fall, newish plaster). But was wondering if there is something else I’m missing, or other things I can adjust to help the pH. And also I’m trying to figure out why I almost never hit a target pH with my acid. Thanks for the your help!

 

[mknauss]

Pentair ScreenLogic panel and app.

So you have either an Easytouch or Intellicenter.
In either, you can schedule Spillway. You only need to run water through the spa for 15-30 minutes once or twice a day to keep it chlorinated. Spillway pushes water to the spa and suction from the pool. When you post up pictures of your equipment pad, we can see if you have a make up line that is now sending water to the spa or if the actuated valve is partially open to the spa return.

Read your ET or Intellicenter manual. Look for Spillway.

 

[CrystalRiver]

If you want to know whether you actually reached your target pH after an addition, you need to check it 30 minutes after dosing. If you wait until the next day to test, it may have bounced up again, especially with new plaster and water features running that whole time.

 

[Hchang]

So you have either an Easytouch or Intellicenter.
In either, you can schedule Spillway. You only need to run water through the spa for 15-30 minutes once or twice a day to keep it chlorinated. Spillway pushes water to the spa and suction from the pool. When you post up pictures of your equipment pad, we can see if you have a make up line that is now sending water to the spa or if the actuated valve is partially open to the spa return.

Read your ET or Intellicenter manual. Look for Spillway.

Ok, I will look into that. And I will post pictures tomorrow. I believe it is a Intellicenter and that it’s an actuated valve. But I’ve never seen Spillway anywhere in our app or on the controller by the equipment. It was explained to us that we can only really turn it off by putting it in spa mode. I’d like for that to be wrong, honestly. But that’s how we currently operate it. And our spa mode runs at 3450 rpm so even higher than our “high mode” for the pump.

 

[jark87]

I struggled with pH bounce for years. I always assumed that the SWG was a contributor, as some point to the aeration caused. I removed my fountain in the spa, which helped. I also only have a single pump, thus my spa waterfall cannot be regulated independently. Plus, I like the look and sound of the water over the slate - that’s why we built it.

Having said all that, advice I received on this forum was to let TA settle to a natural reading, which is 60 for my pool. I had been keeping it between 80-100. Once TA was down, my pH bounce isn’t quite as severe, but it still drifts upwards over the course of a week. I usually add a pint of MA every week and all is good. During the winter, when the SWG is hardly running, it’s more like once a month.

 

[Hchang]

If you want to know whether you actually reached your target pH after an addition, you need to check it 30 minutes after dosing. If you wait until the next day to test, it may have bounced up again, especially with new plaster and water features running that whole time.

Ok that’s good to know! I know pH will naturally drift and I know some things that contribute. But I’m looking for more stability than less than 24 hours. I feel like having to add acid every other day is a bit atypical? I will definitely addressing the waterfall and pump issues.

 

[Hchang]

I struggled with pH bounce for years. I always assumed that the SWG was a contributor, as some point to the aeration caused. I removed my fountain in the spa, which helped. I also only have a single pump, thus my spa waterfall cannot be regulated independently. Plus, I like the look and sound of the water over the slate - that’s why we built it.

Having said all that, advice I received on this forum was to let TA settle to a natural reading, which is 60 for my pool. I had been keeping it between 80-100. Once TA was down, my pH bounce isn’t quite as severe, but it still drifts upwards over the course of a week. I usually add a pint of MA every week and all is good. During the winter, when the SWG is hardly running, it’s more like once a month.

Thank you! I would be happy with adding once a week! Right now it’s every other day and I never get where it should be. Thanks for your perspective. I may be running my waterfall and pumps to high or for too long. But I agree with you, we built the water fall to enjoy!

 

[CrystalRiver]

Every other day with new plaster is very typical. It will calm down over the next ~year as the plaster cures.

 

[mknauss]

But I’ve never seen Spillway anywhere in our app or on the controller by the equipment.

Page 51 of your Intellicenter User Guide.

 

[Hchang]

Page 51 of your Intellicenter User Guide.

I apologize, I am not at home. But after looking at the manuals online, we have Easy Touch. I read through it a bit, but don’t exactly see what to do. Right now, we control everything from the ScreenLogic phone app. Under Pool we have options to run the pump “pool high” or “pool low”, and the heater. Under the spa we have “spa” and “air blower” and the heater. then we can also control lights of course. Under the Features we have “aux 3”, which is not attached to anything. We were told this could eventually be connected to landscape lighting for example. I am attaching images of the app. Not sure if that helps. Would I add a circuit called “Spillway”? I have a feeling you would need to see the equipment still to help me with this! I will take a picture in the morning. I would love to be able to independently turn off the spillway/waterfall but still have the pool circulating. Thank you so much!

 

[mgtfp]

CYA of 48 was admittedly an estimate on the cylinder that came with my TFT-100. It was reading between 45-50.
I don’t know the readings of my fill water, that’s a good idea to test. thank you.

I can add pictures of equipment when I’m home tomorrow.
thank you!

Not worth bothering to interpolate between the graduation marks. The scale is logarithmic, not straight forward to read in-between the lines. If the dot disappears between 40 and 50, just round up to 50 and call it a day.

One more thing to consider, is to make sure to compare pH-readings at the same points within the chlorination cycle. When we say that bleach is pH-neutral, that means that the chlorination cycle is pH-neutral. When you add bleach, pH will rise. Once FC is back to where it was before adding bleach, that pH-rise will be compensated, as the "use" of chlorine (by killing germs, oxidizing stuff and by UV-decay) is an acidic process. Without the pH-drift by CO2-outgassing, pH would be back where it started.

That means that if you allow large FC-swings by letting FC come down to below min (with CYA 50, your min FC is 4, but you seem to let it come down to 1.5) and then adding a big splash of bleach, you will also have a considerable pH-swing withing your chlorination cycle (not a drift, but a cycle). If you start at pH 7.6 and add 81oz of 12.5% bleach (from your PoolMath log), pH will be nearly up at 8 (assuming TA 60). Starting at pH 7.9, these 81oz would get you up to 8.3. That is not due to the CO2-outgassing drift. But you might misinterpret this as part of the drift when comparing pH-readings taken at different points within the chlorination cycle.

Try not to let your FC go below min (which you should anyway as you are at risk of an algae bloom by allowing FC drop below min). Add smaller quantities of bleach more often, and always compare pH-readings from the same point in the chlorination cycle when estimating the pH-drift.

The effect on pH directly after adding chlorine gets sometimes forgotten, and that the statement of bleach being pH-neutral has to be seen over the complete chlorination cycle. Here a quick refresher from Chem Geek:

Adding chlorine DOES raise the pH, but when the chlorine gets used/consumed the pH drops back down. Specifically, starting with your numbers I calculate that the pH would have risen from 7.6 to 8.2. Also, if you read the pH test fairly quickly, then 13.6 ppm FC isn't going to give you a false reading. Your pH is very likely to be at 8.2 if your initial reading was correct (not sure why you think it's 7.8).

So if you intend to keep the FC higher and not let it fall, because of your higher CYA level, then yes you should add some acid to lower it. You could wait for your FC to drop to 10 ppm or so before checking the pH again and then adding acid just to play it safe, but I see nothing inconsistent in your numbers.

Again, hypochlorite sources of chlorine DO raise the pH upon addition. They are only close to pH neutral when the added chlorine is consumed/used. This means that ongoing use of such chlorine doesn't keep having the pH go up and up, at least not quickly (there is a small amount of excess lye in chlorinating liquid and bleach). However, in your situation, you are raising the FC fairly permanently so the rise in pH from your chlorine addition will also be fairly permanent and therefore needs adjustment by adding acid to lower the pH.