Strange PH readings

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simonmoll

simonmoll

0
Feb 17, 2014
51
Barbados
I have been using TFP for a couple of years now and have not had a green pool for a long time :).
All I do is use a Taylor 100 kit and test for chlorine and PH every morning and add bleach acid as needed. Very occasionally I do a full test but all it tells me is what I already know!
However something funny happened the other day.

I looked at the PH and it was high around 8-8.2+. So I shook the tester violently and the PH went to 7.2.
I tried this a few times over the next few days and the same happened. But not today it showed 7.6 and stayed there after vigorous shaking so I am completely flummoxed!

I am sure all is ok just wondered if anyone else had had this happen and whether a vigorous shake rather than a couple of flicks of the wrist is really needed?
 
simonmoll said:
I have been using TFP for a couple of years now and have not had a green pool for a long time :).
All I do is use a Taylor 100 kit and test for chlorine and PH every morning and add bleach acid as needed. Very occasionally I do a full test but all it tells me is what I already know!
However something funny happened the other day.

I looked at the PH and it was high around 8-8.2+. So I shook the tester violently and the PH went to 7.2.
I tried this a few times over the next few days and the same happened. But not today it showed 7.6 and stayed there after vigorous shaking so I am completely flummoxed!

I am sure all is ok just wondered if anyone else had had this happen and whether a vigorous shake rather than a couple of flicks of the wrist is really needed?
Click to expand...

What's your FC level at?


Sent from my iPhone using Tapatalk,16k gal SWG pool (All Pentair), QuadDE100 Filter, Taylor K-2006
 
FC 5.5
CC 0.0
PH 7.2 after vigorous shaking 8.2 before??
TA 40
CH 625
CYA No reading (0.0) maybe the chemical has gone off?

So am thinking it is low TA that may be causing this. Will sort that out and test again.
 
simonmoll said:
FC 5.5
CC 0.0
PH 7.2 after vigorous shaking 8.2 before??
TA 40
CH 625
CYA No reading (0.0) maybe the chemical has gone off?

So am thinking it is low TA that may be causing this. Will sort that out and test again.
Click to expand...

It's not your TA that's the problem. Mine is nearly just as low as your TA and I tried replicating your problem. No amount of vigorous shaking changes the color of my pH test at all.

You are also showing a CYA of 0 which is really only possible on a fresh fill. Otherwise, if it's low, it's just less than 30ppm as that's the lowest possible reading for the test. A low CYA is not good as that makes your 5.5 ppm FC very harsh.

If your reagents are old, I'd suggest new ones before you go balancing your water. Then, with new reagents in hand, get your water properly set to the recommended levels and see if the pH test still is a problem.


Sent from my iPhone using Tapatalk,16k gal SWG pool (All Pentair), QuadDE100 Filter, Taylor K-2006
 
At low TA levels, the PH tends to swing around wildly.
Click to expand...
pH and TA are easily the most misunderstood and mysterious of the parameters we test....lots of misconceptions and assumptions that are not quite true.

I don't think the collective forum experience demonstrates the statement above to be true. Changing it from "tends to" to "may" is probably better wording.

Pool School will always be a work in progress and needs to be tweaked often to provide the most accurate information.

All that said, I don't think that statement is relative to the thread, is it?
 
duraleigh said:
pH and TA are easily the most misunderstood and mysterious of the parameters we test....lots of misconceptions and assumptions that are not quite true.
I don't think the collective forum experience demonstrates the statement above to be true. Changing it from "tends to" to "may" is probably better wording.
Pool School will always be a work in progress and needs to be tweaked often to provide the most accurate information.
All that said, I don't think that statement is relative to the thread, is it?
Click to expand...

one person thinks low TA may be causing the wild TA swings, another person says no. i thought pool school, which everyone tells us to refer to, could help with this subject.

pool school's message may not be correct (how am i to know?), but this messenger's heart was trying to help out.

if pool school is wrong, then i hope it will be corrected.
 
Every pool is different. Pool school is pretty darn close...close enough for most to learn
how their pool reacts to chemical additions, but it can't be 100% accurate that would be impossible.

Example:

A lot of folks with plaster pools in the southern regions have ph rising, it's been found and
recommended they could go as low as TA of 50 to help keep the ph steady. Pool math
was even changed a few months back from that. A lot of plaster pool owners in
the south are now not needing to add acid or much less than they had to before

My vinyl lined pool on the other hand has constant falling PH if it is not at least
at TA of 80. Any lower and my ph falls.
 

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Let's not get too far afield here as this is turning into a wild goose chase post. The OP isn't describing a normal situation and has two confounding factors at play here.

First, the reagents used are suspect in age. That alone can cause lots of issues.

The second thing is the OP is doing something you should never do - namely, you should never, under any circumstance "vigorously shake" test solutions. None of the test procedures call for vigorous shaking. All test solutions should be inverted to mix. Two or three inversions is more than enough to fully mix the phenol red indicator.

So while this may be an odd effect (that no one has since replicated) it is not really necessary to hash out possible explanations because (a) we don't know if the regents used are bad and/or (b) it's not all that unusual to expect to get odd results when you don't follow the test procedures properly.


Sent from my iPhone using Tapatalk,16k gal SWG pool (All Pentair), QuadDE100 Filter, Taylor K-2006
 
The Taylor 100 kit was bought in January through Amazon. PH reagent expiry 07/17 so that should not be an issue.
Shaking vigorously or inverting two or three times: should that make a difference to the chemical reaction?

It seems that when FC is low at the end of the (sunny) day that this effect does not happen.
After writing that I went to test: not true.. FC=1 (was 5 same time yesterday) PH 8.2 + until shook vigorously then 7.2! (so don't know whether to add acid or not!!

Anyway my CYA was <30. I said zero because there was virtually no cloudiness at 30. I am going to add stabaliser slowly and see what happens as I am using too much chlorine recently.
Then will get TA to a higher level and see if that helps.
 
simonmoll said:
Shaking vigorously or inverting two or three times: should that make a difference to the chemical reaction?
Click to expand...

The short answer to this is - YES, it is possible.

Shaking the pool water sample vigorously can liberate both dissolved CO2 gas and, to a lesser extent, chlorine. However, both of those processes will generally cause pH to rise, not fall. Mind you, this is only possible in principle as i have not done any calculations to determine the magnitude of the change, it could be immeasurably small.

One practical area where shaking would be ill advised is in the CYA test. You can entrain tiny air bubbles in the solution that can stick to the melamine precipitate and that can make the sample appear cloudier than it really is. This would lead to a false-high result.

At the end of the day, the tests do not require vigorous shaking. Gentle inversion of the sample or hand swirling is more than adequate to mix the reagents. The chemical reactions generally happen very quickly and vigorous shaking will not make them go any faster. If mixing is an issue, one can always purchase a SpeedStir to help with the mixing process.

So, if your reagents are still good, then add the five drops of R-0004 phenol red reagent, invert 2-3 times to mix and determine your pH. Shaking vigorously is not necessary.


Sent from my iPhone using Tapatalk,16k gal SWG pool (All Pentair), QuadDE100 Filter, Taylor K-2006
 
JoyfulNoise said:
One practical area where shaking would be ill advised is in the CYA test. You can entrain tiny air bubbles in the solution that can stick to the melamine precipitate and that can make the sample appear cloudier than it really is. This would lead to a false-high result.
Click to expand...
Looks like the Extended Test Kit Directions need to be updated:
Cap and then shake the mixing bottle for 30 seconds.
Click to expand...

Which is what I've been doing for 2 years :/
 
That really should be better defined. The actual Taylor instructions say -

2. Add R-0013 Cyanuric Acid Reagent to neck. Cap and mix for 30 seconds. Sample will turn cloudy if cyanuric acid is present.
Click to expand...

And by mix, they mean a gentle inversion mix (it's what most chemist-types would understand it to mean).

I will talk to the mods about fixing that.


Sent from my iPhone using Tapatalk,16k gal SWG pool (All Pentair), QuadDE100 Filter, Taylor K-2006
 
I don't recall it mentioned, but I wonder with little to no cya in the water, a FC of 5.5 is extremely harsh and could very well be causing a false high reading of the pH test. Is this a possibility Matt?

It is preached here that FC levels over 10 cause false high readings on the pH test but that should be much more dependent on the CYA level since a FC of 10 with 30ppm CYA is much more concentrated than 10 FC at 80ppm CYA?
 

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