Problems Measuring Ph - Which Test Can I Trust?

[WaterBeast]

Caveat: Cross-posted on Pool & Spa Forum - no disrespect.


Hi,

I have a relatively new spa and am struggling with correctly measuring pH. Simply put, I don't know which test to trust. With the ranges I am seeing below, I am concerned my true PH may be too high and I will have problems with scaling. I badly want to believe in my Taylor test because of the precision relative to other tests, but I think I may be seeing some type of interference.

280 gal Emerald spa
SpaFrog (BCDMH bromine and Silver/Limestone mineral cartridges)
Ozonator
TA 95
Hardness 220
Bromine 4.5 (high today, been targeting 3-4 ppm)
pH: 7.5 - 8.1+, depending on what you believe

pH Tests
1) Taylor K2106 Test Kit dated 12/07: light/bright purple, >= pH 8.0, 2 drops acid demand to get to pH 7.6. This has been consistent over a range of bromine levels, 0.5ppm to >5 ppm. Initially I was adding a lot of pH-, eating up my TA, adding TA+, etc. but eventually I lost confidence in the Taylor test.

2) Taylor K2106 Test 2 (assuming Bromine interference): Added 1 drop Thiosulfate first. Light/bright purple, > 8.0, 2 drops acid demand to get to pH 7.6. I've done tests in the past with 2 drops Thiosulfate, same result. I have bromine tested a water sample treated with Thiosolfate and read 0 ppm bromine.

3) Aquacheck Red Test Strips: pH 7.2-7.8, estimating 7.5 in color gradient. This is the test I have been believing and managing my pH against.

4) Nature2 Test (bought to try to get another read on things): pH 7.9. The first time I tried it the color seemed purple like the Taylor test.

5) TetraTest pH (sodium hydroxide / phenolphtalein / ethyl alcohol; yellow = 5.0, light blue = 7.5, purple = 10.0): pH ~8.1. I wanted to use a different totally test so I bought a non-strip pond test kit that handles a wide pH range.

6) I took a water sample to a dealer on 4/21 for a test, whu used an (AquaCheck?) test strip and an electronic reader. Results: TA 80, pH 7.4, Hardness 140, Sanitizer 2.8. This is part of what made me stop believing in the Taylor test.

I read about Iron interference on the Taylor literature - could the silver or something else be affecting the test? I've considered using a metal sequestering agent, but I think this would eliminate one of the benefits of the SpaFrog mineral cartridge.

I'd really appreciate your thoughts on this. I'm happy to provide more info if required.

PS> I read TA: What is it really and got to thinking that maybe the Taylor test is right and my TA increasing, pumping/aeration, and mineral limestone cartridge are contributing to a bona fide high pH. But, if I am wrong and I fix what isn't broken, I risk corrosion of my equipment. Hmmmm....

Waterbeast

 

[257WbyMag]

Welcome to TFP!

The experts will be by shortly to fully answer your question. One thing that strikes me though about the dealer test using the Aqua Test analyzer where you got a pH of 7.4 is this...I believe that your pH in that sample could possibly be reading lower due to agitation of the sample in transport to the dealer. If the sample was bumped around or shaken during transport, this might cause CO2 outgassing from the water and the result would be a lower pH than what you might pull directly from the spa. I would tend to side with the Taylor test results.

Waterbear, duraleigh, etc, what do you guys think? Or am I backwards in my thinking?

Craig

 

[257WbyMag]

Yep, I am backwards. Outgassing would cause to pH to rise, not fall. :?

Stumped.

Craig

 

[JasonLion]

Very high halogen levels (chlorine/bromine) will cause the Taylor PH test, and other Phenol Red based tests, to read an unusual color, similar to the 8.2 color, even when the PH is reasonable. Colors are difficult to describe in words, both the usual PH 8.2 color and the high halogen interference color look purple to me, though they do look different in a way I can't really describe.

However, it makes sense that your PH would be around or above 8.0. The large amounts of aeration in a spa combined with TA around 95 will rapidly drive the PH up above 8.0. Also, bromine at 4.5 is no where near high enough to cause problems with the PH test, and your check with adding Thiosulfate would likely have changed the PH reading if there was high halogen interference. The fact that Thiosulfate had little if any effect suggests the PH reading is correct around 8.0.

Test strips are not at all reliable, even when read by "fancy" electronic readers. They are very sensitive to how long they are submerged and how excess water is removed and so even the best of them produce rather variable readings.

A metal sequestering agent would interfere with the Spa Frog. Of course I don't think the Spa Frog is such a good idea in the first place. In any case nothing the Spa Frog adds will cause problems for the PH test.

 

[WaterBeast]

I went back to my records. Earlier when I was believing the Taylor test results, I was treating with significant amounts of pH- and later Muriatic Acid (carefully) when I ran out of pH-. This reduced pH and TA. When the Taylor test started looking more reasonable (< 7.8), I stopped for the day. The next day the Taylor test was 'purple' / 8.0+ again but the Aquacheck strip test was showing 7.2. That's when I got nervous, took the test sample to the dealer and got the 7.4 reading. Later that day I tested again: Taylor purple / 8.0+, newly purchased Nature2 strips 8.0+, and lost confidence in these tests.

I have a larger set of test kits now than I had earlier when I began to doubt the Taylor tests, and now the preponderance of evidence is pointing back towards the higher pH value being the correct value. Tomorrow I'll try to get a water sample to a different dealer, but I suspect they all use the quick and dirty strip/reader tests.

I REALLY want to have an accurate and more importantly trustworthy pH testing mechanism. I'm enjoying managing the water chemistry or my spa, and tryign to keep the saturation index as low as possible, but this lingering doubt is killing me.

WaterBeast

 

[JasonLion]

The Taylor Phenol Red PH test is one of the best ones out there and the situations in which it is wrong are fairly unlikely. The next step up would be the ColorQ, which can read the colors more precisely but suffers slightly more from high halogen level interference. To do better than that you need a lab grade meter and calibration solutions that are calibrated against and replaced frequently. The lab equipment can be fun to play with but it really isn't needed for a spa or a pool. Worse, if you don't do the calibrations frequently and correctly then the lab meter can be way off, a problem that some of the pool stores have.

With TA around 95 it doesn't take the spa jets all that long to bring the PH up to above 8.0. That will continue to be true as long as your TA is high. That is actually a standard you can measure your tests against, if you run the jets for an hour or two and the test doesn't read above 8.0 then something is wrong with the test. If you really want to keep your saturation index under control you will need to lower TA significantly.

 

[Guest]

Trust the Taylor. You are using bromine so don't stress about getting the pH to 7.6. Anything below 8.0 is going to be fine and with CH at only 220 I would not worry that much about scaling.

 

[Sabot]

Just to add:

I just purchased and have started using the Oakton Portable Waterproof pHTestr 30. I also use the ColorQ7 Pro. I test my water with both of them daily. So far, the ColorQ is reading a it higher then the pHTester 30 by .2 on average. (i.e. ColorQ may read: 7.6 and pHTestr may read: 7.4) Both units have a +/- built into their tests. I purchased the Oakton Portable Waterproof pHTestr 30 with Calibration Kit for $140 plus freight. You need to calibrate it weekly. I also purchased a pint of Oakton pH 4.01, 7 and 10 Calibration Buffer Solution Bottle at $9.75 ea. The caibration takes only a few minutes and is simple. Waterbear, between the ColorQ and the pHTester 30 which one do you believe to be more accurate?

I have closed down my spa for the summer months but I did use the ColorQ to test the spa water. I only used the BBB method in my spa this year and it worked great. I did have to check it daily and make adjustment. I learned that when using BBB on my spa, I needed to check it daily when it was in use daily. I could stretch it to every two or three days when no one was using it.

 

[Guest]

Hard call, neither is what I would call a really top quality unit but both are certainly accurate enough for pool use. I would not lose sleep over a .2 difference in pH. Personally, I would lhave gotten the Oakton Acorn pH meter but it it over twice the price of the one you got.

 

[Sabot]

I really look hard at that one after you recommended it to me. I am treading a real fine line with the Mrs. since I have been buying a few pool techno gadgets. I have a few more gadgets which I am purchasing for my Liquidator/pH Adjuster project. I am glad the pool is her project! I have been through the ringer on my fishing boat project and it is no fun.

Oakton Acorn® pH 5 Portable pH Meter with pH Electrode and Temperature Probe.
pH Range: 0.00 to 14.00 pH, ±0.01 pH (resolution 0.01 pH)
Temperature Range: 0.0 to 100.0°C, ±0.5°C (resolution 0.1°C)
ATC: manual or automatic from 0.0 to 100.0°C
The Acorn series meter is a rugged compact meter with built-in stand in the boot. Toggle between pH and temperature in °C with a press of a button.
Includes: pH electrode (WD-35801-00), temperature probe (WD-35613-05), protective rubber boot, batteries, and instructions.
View Datasheet

Price: $232.00

 

[Guest]

Just keep in mind we are talking about a swimming pool and NOT a science experiment. Remember that REALLY GOOD pH meters cost quite a bit more than either of these Oakton units (You will easily spend about $500 or more for a laboratory quality bench meter.) However these portables are, IMHO, more than enough for either pool or aquarium use! I have used some of the Oakton meters and they are dependable and rugged units.

The Oakton portable I mentioned is $285 for the complete kit and if you want a waterproof one you will spend over $500 for a model 300!

 

[TomU]

I'm planning on purchasing one of these pH meters: PH-200
It has an accuracy of +/- .02. That seems a lot better than the other testers I've see out there. I've found it at here for $84.99. I seem to always have difficulty determining exactly which color is the closest on the normal pH test. I wish someone had a pH test that worked like the TA, or CL tests (changing from one color to another).

 

[Sabot]

That is the hardest part for me... I have to say three times "it's not a science experiment...","it's not a science experiment...","it's not a science experiment..."

But the gadgets are so much fun to play with! I will stick with this for now. I will PM you when this breaks to find out the latest greatest meter! As always, thanks for your input and that yellow hummer fits you just right!

 

[WaterBeast]

Wow, thanks for all the feedback. I carefully re-ran all my tests today assumign the Taylor test is correct and checking the color reads of the other tests carefully and had my wife independently check colors in parallel. Results:

Taylor pH: pH > 8.0, 3 drops acid demand to get to pH 7.5
TetraTest: 8.1; My wife gave the exact same pH assessment based on comparing the liquid color to the color card which is calibrated in 0.5 increments. This test is actually pretty nice in terms of color range and breadth of pH values tested, and seems to be the best correlation of the taylor test.
Aquacheck: pH > 7.8. I find this color quite difficult to read and am now thinking that I have probably been mis-reading this strip test as a 7.2-7.8 value. I'll keep cross-checking the strips against the taylor test, and comparing to the other strip tests.

So, I decided to lower the pH using dry acid. Running the math from the taylor booklet it came out to 1.03 oz for a 280 gal tank for 3 drops acdi demand. I added 1 oz in 1/2 oz increments waiting 3-0+ minutes between tests. Bingo - the Taylor test now reads 7.5 and my TA appears to have dropped from 95 to ~80. The strip test still appears to be a 7.2-7.8 value but I am still strugglign a bit on the color interpretation.

Observations:

1) I am having a real challenge reading the various strip tests. It seems that I need an independent test that is accurate and that I believe in (like the Taylor pH test) to help calibrate my eye against the strip and the color chart.

2) My earlier attempts to lower the pH with the liquid pH- (I am not using dry acid) seemed to take a ton of 1oz (per bottle recommendations) additions, and these many small additions seemed to really eat up my TA. The dry acid nidely reduced the pH with minimal reducation of TA.

I really appreciate the help. I have seen some references to strip tests that are easier to read, I may try to obtain some of these. I'd like to have something simple that I can get my wife to do, as she seems to have limited tolerance for the Taylor kit. Myself, I love my new spa / mini-chemistry set!

WaterBeast

 

[Guest]

I'm planning on purchasing one of these pH meters: PH-200
It has an accuracy of +/- .02. That seems a lot better than the other testers I've see out there. I've found it at here for $84.99. I seem to always have difficulty determining exactly which color is the closest on the normal pH test. I wish someone had a pH test that worked like the TA, or CL tests (changing from one color to another).

after looking at the website their line looks suspiciously like rebranded Oakton or Eutech units! (Oakton and Eutech are the same, btw.)

It is not possible to titrate a pH test unless you are trying to determine a set pH (which is what the TA test actually is). If you are testing a range of pH then you are stuck using indicators. Phenol red that is used in pools ia actually one of the easier ones to read!

 

[Guest]

Wow, thanks for all the feedback. I carefully re-ran all my tests today assumign the Taylor test is correct and checking the color reads of the other tests carefully and had my wife independently check colors in parallel. Results:

Taylor pH: pH > 8.0, 3 drops acid demand to get to pH 7.5
TetraTest: 8.1; My wife gave the exact same pH assessment based on comparing the liquid color to the color card which is calibrated in 0.5 increments. This test is actually pretty nice in terms of color range and breadth of pH values tested, and seems to be the best correlation of the taylor test.
Aquacheck: pH > 7.8. I find this color quite difficult to read and am now thinking that I have probably been mis-reading this strip test as a 7.2-7.8 value. I'll keep cross-checking the strips against the taylor test, and comparing to the other strip tests.

So, I decided to lower the pH using dry acid. Running the math from the taylor booklet it came out to 1.03 oz for a 280 gal tank for 3 drops acdi demand. I added 1 oz in 1/2 oz increments waiting 3-0+ minutes between tests. Bingo - the Taylor test now reads 7.5 and my TA appears to have dropped from 95 to ~80. The strip test still appears to be a 7.2-7.8 value but I am still strugglign a bit on the color interpretation.

Observations:

1) I am having a real challenge reading the various strip tests. It seems that I need an independent test that is accurate and that I believe in (like the Taylor pH test) to help calibrate my eye against the strip and the color chart.

2) My earlier attempts to lower the pH with the liquid pH- (I am not using dry acid) seemed to take a ton of 1oz (per bottle recommendations) additions, and these many small additions seemed to really eat up my TA. The dry acid nidely reduced the pH with minimal reducation of TA.

I really appreciate the help. I have seen some references to strip tests that are easier to read, I may try to obtain some of these. I'd like to have something simple that I can get my wife to do, as she seems to have limited tolerance for the Taylor kit. Myself, I love my new spa / mini-chemistry set!

WaterBeast

Test strips are referred to as 'guess strips' for a reason. They are pretty much worhtless for pool pH. Using a drop based kit for pH is the best and easiest way to get an accuracte ph reading. You are NOT going to get that from a strip. Even a cheap $7 two way test kit will give more precise pH readings than even a Taylor test strip, which has the best pH test, IMHO, but it still leaves a LOT to be desired.

Lowering pH WILL lower TA, can't be helped. and vice versa. Don't matter if you are using dry acid or a liquid acid like muriatic or sulfuric. Perhaps this thread might help clear up why for you. (then again it might not if you don't have a handle on the chemistry.)

 

[sredish]

more discussion on the pocket testers, what about some of the LaMotte ones? EDIT: looks just like the Oakton unit I just googled... hmmmm says .01+/-

 

[sredish]

or the Lamotte Tracer

 

[TomU]

after looking at the website their line looks suspiciously like rebranded Oakton or Eutech units!

I just got off the phone with the company and they said they are an OEM and do not rebrand anyone else's products. They also gave me a link to an nice comparison page between their TDS meter and other's. Here is the link.

 

[hmdigital]

I'm planning on purchasing one of these pH meters: PH-200
It has an accuracy of +/- .02. That seems a lot better than the other testers I've see out there. I've found it at here for $84.99. I seem to always have difficulty determining exactly which color is the closest on the normal pH test. I wish someone had a pH test that worked like the TA, or CL tests (changing from one color to another).

after looking at the website their line looks suspiciously like rebranded Oakton or Eutech units! (Oakton and Eutech are the same, btw.)

It is not possible to titrate a pH test unless you are trying to determine a set pH (which is what the TA test actually is). If you are testing a range of pH then you are stuck using indicators. Phenol red that is used in pools ia actually one of the easier ones to read!

Hi, Rob from HM Digital here. We are the original manufacturers of all of our products and Oakton (Eutech) is actually one of our major competitors. In person, the products definitely look different and the more important issue is that our products' specifications and features are superior to the competition (and a better price!). These products are all waterproof and all recommended for pool testing:

COM-100 (EC/TDS/Temperature)
PH-200 (pH/Temperature)
ORP-200 (ORP/Temperature)

A common question is if we make a combo meter for these parameters. We do not for two reasons: 1) It's possible that the different sensors can conflict with each other and give false readings (such as pH with conductivity); and 2) If you have a combo meter and it breaks, you're out all the parameters. Our prices are excellent and our testers combined are comparable in price to a competitor's combo meter.

We are located in Los Angeles and a live person always answers the phone. Please do not hesitate to call with any questions! Our products are available through a number of distributors and web stores around the country.

Thanks to Tom U. for telling me about this forum!