pH will not go below 8.2

Yellarcat

Member
Jul 15, 2017
18
Baton Rouge LA
I have a new plaster pool and for the past 3 months I have been trying to balance my water chemistry. I have everything tuned in perfect except for pH. For the last month, no matter what I do or how much acid I add, it will not go below 8.2, even when I add the amount of acid that pool math says will drop it to 7.0. I add the acid and check it the next day and it hasn't changed. The water is clear though.

Below are my latest test results and chemical additions:

------------------------------------------
Build Type: Plaster
Volume: 2850 gallons
------------------------------------------
Latest Test Result Summary:
FC: 5.0 (22 hours ago)
CC: 0.0 (22 hours ago)
pH: 8.3 (22 hours ago)
TA: 70 (2 days ago)
CH: 450 (2 days ago)
CYA: 40 (2 days ago)
TEMP: 78° (2 days ago)
CSI: 0.71 (22 hours ago)
==========================================
------------------------------------------
Test Results 05-17-2020 @ 03:05 PM
------------------------------------------
Free Chlorine: 5.0
Combined Chlorine: 0.0
pH: 8.3
CSI: 0.71
------------------------------------------
Chemical Addition 05-16-2020 @ 04:15 PM
------------------------------------------
+ 11.8 FluidOunces of MuriaticAcid29
+ 16 FluidOunces of Bleach
------------------------------------------
Test Results 05-16-2020 @ 03:36 PM
------------------------------------------
Free Chlorine: 0.5
Combined Chlorine: 0.5
pH: 8.3
Total Alkalinity: 70
Calcium Hardness: 450
CYA: 40
Temperature: 78°F
CSI: 0.71
------------------------------------------
Chemical Addition 05-13-2020 @ 02:24 PM
------------------------------------------
+ 6.7 Ounces of BakingSoda
+ 51 Ounces of CalciumChloride
+ 9 FluidOunces of MuriaticAcid29
+ 10 FluidOunces of Bleach
------------------------------------------
Test Results 05-13-2020 @ 01:18 PM
------------------------------------------
Free Chlorine: 2.5
Combined Chlorine: 0.5
pH: 8.2
Total Alkalinity: 60
Calcium Hardness: 325
CYA: 40
Temperature: 78°F
CSI: 0.39
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
37,016
Laughlin, NV
Pool Size
6000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
Can you let us know what test kit you are using?
 

ping

TFP Expert
LifeTime Supporter
Jun 24, 2011
3,144
Long Beach, CA
Don't wait until the next day to test the pH after adding the acid, test it about 30 minutes later.

Please clarify the strength of the acid 15% or 32%?
 

Yellarcat

Member
Jul 15, 2017
18
Baton Rouge LA
I use the TF-100 Test Kit with the optional digital ATC pH tester, calibrated per instructions. Source tap water reads 7.2 pH.

I use the Home Depot HDX muriatic acid, which is 31.45% hydrogen chloride. It appears I have incorrectly been recording 29% acid instead of 32%.
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
37,016
Laughlin, NV
Pool Size
6000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
New plaster will drive up the pH. Keep reducing it as per your start up procedure.
 

kevinskii

Gold Supporter
Aug 6, 2019
170
Los Angeles, CA
Pool Size
1
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
Is your pool really 2850 gallons? Just making sure there isn't a typo in the PoolMath app. If it is actually a 28,500 gallon pool then 11oz (roughly 1/10th a gallon) of acid probably won't do much. It take me roughly half a gallon to bring the pH down about 0.5 in my 18k gallon pool.
 

Yellarcat

Member
Jul 15, 2017
18
Baton Rouge LA
No, that’s not a typo. It’s really 2,850 gallons. It’s a small little cocktail plunge pool. Pool math works to dial everything in but pH.

I just added enough acid according to pool math to drop it down to 7.0 and checked it after 2 hours and it is still at 8.3. Didn’t move at all....
 

JamesW

TFP Expert
Mar 2, 2011
23,856
Don't add any more baking soda.

With a pool that small, you can retest in about 30 minutes and add more as needed.

What pump do you have and how much is your flow rate?
 

kevinskii

Gold Supporter
Aug 6, 2019
170
Los Angeles, CA
Pool Size
1
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
Also, are you aerating the water much, with a waterfall maybe? I don't think it would cause the pH to increase so rapidly, but it would be good to know.
 

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Yellarcat

Member
Jul 15, 2017
18
Baton Rouge LA
Something definitely isn't adding up.

I added more acid yesterday and took another after a couple of hours and it hadn't moved, still 8.3. Added more this morning, checked and it is still saying 8.3.

So I double check it with the K-1000 drop test and the color looks orangyish like the 6.8 level comparison. Hmm, maybe the pH meter is stuck or broken so I use it to check my tap water and it says 7.4. So not stuck. Double check the tap water with the drop test and the color of the tap water is purplish like the 8.2 comparison. Aarrrggg!!! Nothing lines up. They are contradicting each other at opposite ends of the scale. That makes no sense.

Is there a more reliable way to test pH like there is with chlorine where you can count the number of drops until it turns color? The color comparison is too ambiguous and the pH meter appears to be unreliable.

My pump is a Tristar VS 900 Omni operating at a 35 GPM flowrate. I don't have any aeration. Eventually it will have a waterfall but it's not hooked up yet.

Also, what is the thinking behind not adding any baking soda when pool math tells me to?
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
37,016
Laughlin, NV
Pool Size
6000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
You need soda ash - NOW. If you have a heater you are dissolving it.
 

Yellarcat

Member
Jul 15, 2017
18
Baton Rouge LA
Thanks to everyone who has responded. You all have been very helpful.

Yesterday, I added an amount of washing soda that pool math says should raise my pH from 6.8 to 7.5. When I checked it later with drops, the color is somewhere between 7.8 and 8.2, maybe in the middle. It's hard to tell but it is definitely more than 7.5.

I have ordered a bottle of 7.0 pH reference solution to see if a can keep a meter dialed in with. I calibrated my existing pH meter with the one packet of reference it came with but obviously somewhere along the way it went off, either it's broke or it needs to be recalibrated.

Is there any more precise way to test pH (the drop color range seems to wide) that is also reliable? Or does anyone recommend a digital pH meter that is good if I routinely check for calibration?
 

rumcglot

Silver Supporter
Feb 13, 2019
100
Texas
Is there any more precise way to test pH (the drop color range seems to wide) that is also reliable? Or does anyone recommend a digital pH meter that is good if I routinely check for calibration?

I have one of the kits with the acid demand reagent from Taylor... bought before my TF-100. It won't give you precise pH; although, if you know some chemistry maybe it would. Instead, it tells how much acid you need to get the pH desired. That can give you a subjective feel for how much over 8.2 the sample is and acts as a check on the calculation done in the PoolMath app.
 
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