Alkalinity won't go down...

Kevinr14

Well-known member
Mar 8, 2021
109
Phoenix, AZ
Pool Size
15000
Surface
Plaster
Chlorine
Liquid Chlorine
Hi all. I'm new here but I've done tons of reading. I am dealing with my first pool in a house i purchased last month. It is an outdoor diving pool calculated at about 15,000 gallons. I have a new tf100 test kit and I've been following the instructions precisely when testing.

My alkalinity has been a bit high between 120 and 140ppm. My PH keeps increasing and the pool is not being used. The water temp has been around 60 to 65 Fahrenheit. CYA is at 30ppm. I've been using only 10% liquid chlorine as a sanitizer so i do not raise the cya too much. The pool was resurfaced 3 months ago with pebble tec which I've read can affect ph and alkalinity for at least a few months.

Here's what I've done and where i started in regards to ph and alkalinity.

On 3/13, alkalinity was 130ppm and ph 8.0. I used the pool calculator and added 41oz of 14.5% muriatic acid. Later that day, i retested and PH was 7.8 and alkalinity 120ppm. I added another 16oz of acid. Several hours later, i was at 7.6 PH but still 120ppm alkalinity.

Yesterday, 3/16, i tested alkalinity at 140ppm and ph at 7.8. I added 41oz of acid again which brought it down to 130ppm alkalinity and 7.6 PH.

Today, 3/17 alkalinity was 130ppm and 7.6 ph. Per the calculator, i added 72oz of acid again and brought the ph down to 7.3 with the intent to aerate and bring it back up. The problem is that even after 72 ounces of acid, the alkalinity only went down to 120ppm.

If i keep adding acid to reduce alkalinity, won't my ph drop too low? How can i decrease alkalinity without decreasing ph too much at the same time?

Thanks for any help!
 

mknauss

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May 3, 2014
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Laughlin, NV
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Pentair Intellichlor IC-40
Welcome to the forum!

The above article has a great review on Total Alkalinity.
What you are doing, lowering pH, aerate to raise pH, then lowering pH again with acid, and repeat, is how you lower TA.

I suggest you read ABC's of Pool Water Chemistry.
 
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HermanTX

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May 20, 2020
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Katy TX
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Today, 3/17 alkalinity was 130ppm and 7.6 ph. Per the calculator, i added 72oz of acid again and brought the ph down to 7.3 with the intent to aerate and bring it back up. The problem is that even after 72 ounces of acid, the alkalinity only went down to 120ppm.
Your calculations are pretty much spot on - with 72oz of 14.5%MA and 15kgals - the pH will decline 0.6 and TA by 9.4 - per Pool Math. So a drop from 130 to 120 on TA in your testing is accurate. So you just need to keep the same process until you get TA to your desired level.
You may want to test your fill water because most likely has TA and if you are adding water then you are counteracting your efforts to reduce TA.
 
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cowboycasey

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Jul 3, 2013
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Southern OK
it will get there.. drop your PH to 7.2 then wait till it reaches 7.8 and do it again, it is a process over weeks not hours :)
 
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Newdude

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Jun 16, 2019
6,820
NY
Each full cycle lowers the TA by about 10, so have a beverage and keep at it. You’re doing great.
 
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Kevinr14

Well-known member
Mar 8, 2021
109
Phoenix, AZ
Pool Size
15000
Surface
Plaster
Chlorine
Liquid Chlorine
Thanks everyone. I have another question though..it seems the alkalinity was increasing on its own even after adding acid previously. If i lower it then take a few days to aerate to bring ph back up, what do i do if alkalinity increases right back to where it started during that time?
 

cowboycasey

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Check your fill water as it may be high... so it raises your TA when you fill.. The other is testing procedures.... Do you have a smart stir, they work great and come out the same every time.. :)

 

Kevinr14

Well-known member
Mar 8, 2021
109
Phoenix, AZ
Pool Size
15000
Surface
Plaster
Chlorine
Liquid Chlorine
Check your fill water as it may be high... so it raises your TA when you fill.. The other is testing procedures.... Do you have a smart stir, they work great and come out the same every time.. :)


I'll test it...I wouldn't be surprised if my fill water (city water) is high TA. If it is, does this mean I'll just always be chasing TA and PH?
 

Casey

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Apr 16, 2007
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I'll test it...I wouldn't be surprised if my fill water (city water) is high TA. If it is, does this mean I'll just always be chasing TA and PH?
Test your fill water n post results. It could very well mean that you'll chase your tail. If you get to 120 or so n your pH stabilizes with no wild swings , then that's just going to be your TA's happy point.

You also said the pool was just refinished 3 months ago. Your pH could be going up because of curing. That should slow down eventually. Just takes time.
 

mknauss

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May 3, 2014
37,018
Laughlin, NV
Pool Size
6000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
I'll test it...I wouldn't be surprised if my fill water (city water) is high TA. If it is, does this mean I'll just always be chasing TA and PH?
Your fill water is most likely Colorado River water. It has a TA of 130 ppm and CH of 250 ppm. So yes, you will be adding muriatic acid about twice weekly from mid April into October. That is due to the fill water used from evaporation. Best if you use softened water for fill up, which removes CH, but does not remove TA.
 
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Kevinr14

Well-known member
Mar 8, 2021
109
Phoenix, AZ
Pool Size
15000
Surface
Plaster
Chlorine
Liquid Chlorine
Your fill water is most likely Colorado River water. It has a TA of 130 ppm and CH of 250 ppm. So yes, you will be adding muriatic acid about twice weekly from mid April into October. That is due to the fill water used from evaporation. Best if you use softened water for fill up, which removes CH, but does not remove TA.

I believe my water comes from the salt river (not actually salty) but i tested it and TA is 120 ppm. Does this mean i shouldn't bother trying to keep the pool below 120ppm as long as ph is within range?
 

mknauss

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TFP Expert
Bronze Supporter
May 3, 2014
37,018
Laughlin, NV
Pool Size
6000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
You will have to keep the TA below 120 ppm or you will never be able to manage your pH and your will have scaling issues quickly with the high CH water.
I find once I get my TA to 80 or so, a twice a week acid addition keeps the TA under control.

I think you get your water from the Salt River Project. Which is the canal from the Colorado River.
 

Kevinr14

Well-known member
Mar 8, 2021
109
Phoenix, AZ
Pool Size
15000
Surface
Plaster
Chlorine
Liquid Chlorine
update: It turns out (after reading more about testing here) that I was actually testing incorrectly. I was not holding the bottles vertically but was holding them horizontally. After learning that, I retested my TA at 100ppm. I tested twice to be sure. Pretty crazy that the size of the drop affects the test that much. I guess it's not as far off as I thought which is good. PH is up to 7.5 today and has been aerating most of the day. I'll check tomorrow and see if it's up to 7.8 yet. I'll add acid again and keep at it until I'm in the ideal range for TA.

By the way, my CYA is at 30ppm. Should I increase that? If so, I'd assume I should wait until after I've got my TA and PH where I want it, correct?

I'm having my single stage pump replaced with a pentair intelliflo vsf tomorrow so I'm pretty excited about that. It should help out my electric bill which can use all the help it can in the summer.
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
37,018
Laughlin, NV
Pool Size
6000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
Good job on the testing. All liquid reagents you must apply with the bottle vertical, little to no pressure on the bottle, let the liquid droplet form and drop off the tip naturally.

I assume you are chlorinating with liquid chlorine? Filling out your signature will really help us help you.
If using LC, then I would leave the CYA as is until mid to late April. Then start adding CYA in 10 ppm amounts every couple weeks until you get to 50 ppm. You may even find 60 ppm is best in the June/July/August timeframe.
 
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Kevinr14

Well-known member
Mar 8, 2021
109
Phoenix, AZ
Pool Size
15000
Surface
Plaster
Chlorine
Liquid Chlorine
Good job on the testing. All liquid reagents you must apply with the bottle vertical, little to no pressure on the bottle, let the liquid droplet form and drop off the tip naturally.

I assume you are chlorinating with liquid chlorine? Filling out your signature will really help us help you.
If using LC, then I would leave the CYA as is until mid to late April. Then start adding CYA in 10 ppm amounts every couple weeks until you get to 50 ppm. You may even find 60 ppm is best in the June/July/August timeframe.

Thanks, I had the info requested in my profile on the left but i also added to my signature. Thanks for all the tips!!

My buddy has had a pool for almost 2 years now and he relies on taking his water to the pool store weekly and they tell him what to add. I guess he had to drain his pool this winter because he couldn't get rid of the algae. I'm guessing his CYA got really high because all he was using was granule shock and chlorine tablets. Based on his experiences, I decided I wanted to learn all I can and not rely on the pool store or a pool service. I've learned so much in the past few weeks and it's great.
 

Kevinr14

Well-known member
Mar 8, 2021
109
Phoenix, AZ
Pool Size
15000
Surface
Plaster
Chlorine
Liquid Chlorine
PH is back up to 7.8 but the pool guys just got here to replace my pump. They recommend not running it until tomorrow in order to let the glue set fully. So i will have to wait to add more acid and start the process again.
 
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Kevinr14

Well-known member
Mar 8, 2021
109
Phoenix, AZ
Pool Size
15000
Surface
Plaster
Chlorine
Liquid Chlorine
Alright, I've been adding acid and aerating the heck out of the pool. I added more acid just a little while ago which according to pool math, should bring TA dowm another 10ppm and I should finally be at 80ppm. Now do i aerate PH back up to 7.5 and leave it there? Or should i leave it at 7.2 and see how quickly it drifts up on its own?
 

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