pH will not go below 8.2

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Yellarcat

0
Jul 15, 2017
22
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:

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Build Type: Plaster
Volume: 2850 gallons
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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)
==========================================
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Test Results 05-17-2020 @ 03:05 PM
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Free Chlorine: 5.0
Combined Chlorine: 0.0
pH: 8.3
CSI: 0.71
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Chemical Addition 05-16-2020 @ 04:15 PM
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+ 11.8 FluidOunces of MuriaticAcid29
+ 16 FluidOunces of Bleach
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Test Results 05-16-2020 @ 03:36 PM
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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
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Chemical Addition 05-13-2020 @ 02:24 PM
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+ 6.7 Ounces of BakingSoda
+ 51 Ounces of CalciumChloride
+ 9 FluidOunces of MuriaticAcid29
+ 10 FluidOunces of Bleach
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Test Results 05-13-2020 @ 01:18 PM
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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
 
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%.
 
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.
 
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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....
 
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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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?
 
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?
 
Yellarcat said:
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?
Click to expand...

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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