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Taylor K-2006 - ph test. Accurate? Interferences?


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Greetings all! I've had my first hot tub for about ten months now, and for this most recent re-fill I'm trying out the Dichlor-then-bleach method. (My last batch of water I only used Dichlor and started having water-cloudiness issues, which I'm attributing either to the way-too-high CYA level or to excessive TA, which I struggled to keep up in the tub manual's suggested 125-150 zone, as well as what became very, very high TDS levels.)

So, for this most recent refill I've added Borates (should be right around 50ppm now) and used Dichlor for the first week or so. My test strips are...inconclusive on the CYA level but I also just got a Taylor K-2006 kit, which is telling me my CYA is just a touch higher than 30ppm. Otherwise my TA is currently 80-90ppm and CH is about 210-220. 

But my big question is this - Taylor K-2006's ph testing. I know, I know, test strips are notoriously inaccurate, and everyone is probably going to tell me to just trust the Taylor kit. But there seems to be a big difference in Taylor's results vs. all my test strips, of which I have like five different brands (for various reasons). 

Those strips all say my ph is quite low right now (after adding Dichlor and MPS yesterday, so it makes sense for the ph to be low because the MPS is acidic, correct?), in the range of 6.6-6.7. I use one of the Aqua Check readers with the TruTest strips, as well as strips from three other companies, and all the others that don't give me a digital reading also return a color hue that says ph is low. 

However, my Taylor test kit says my ph is 7.4. I ran the test twice on the same batch of water and viewed into clear, natural light from the north. 7.4 ph, unmistakable. 

The water then sat for a couple of hours and cooled a little. I just ran the test twice again and Taylor reported a little higher, somewhere between 7.5-7.6 ph. Aqua Check / TruTest strips returned ph values of 6.8-6.9 from the same sample. So cooling the water drove ph up a little, but the gap between the tests and the Taylor kit remains roughly the same. 

So, what's the deal here? What should I trust? Is there anything that might be causing my Taylor kit to read the ph high? Borates, MPS, the tub's temperature, etc.? Or something causing the strips to read low? 

Obviously if the difference were somewhat minimal I wouldn't mind much. But in this case these reading make the difference between adjusting the ph or not. So, any input here? What does everyone think?

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On 2/22/2021 at 3:22 PM, samwise801 said:

The water then sat for a couple of hours and cooled a little. I just ran the test twice again and Taylor reported a little higher, somewhere between 7.5-7.6 ph. Aqua Check / TruTest strips returned ph values of 6.8-6.9 from the same sample. So cooling the water drove ph up a little, but the gap between the tests and the Taylor kit remains roughly the same. 

DId you let the sample sit to cool down or just keep the tub uncovered and get a new sample when the water had cooled?

The MAIN cause of pH rise in a hot tub or pool is outgassing of CO2. If you let your sample sit it would have lost some of it's carbonation (we overcarbonate the water. It's called Total Alkalinity) and the pH would rise as the sample stabilized with the atmosphere. This is normal and it's why we want to test as soon as we collect the sample. As a sample sits the water parameters can and will change.

Another factor is the accuracy vs the precision of the testing method. Accuracy is closeness of the measurements to a specific value, while precision is the closeness of the measurements to each other. The Taylor test using their proprietary phenol red reagent is both accurate and precise. Test strips, while precise (measurements are repeatable on the same sample) are not often accurate (measurements  give correct reading on a known standard test solution). You are seeing this first hand.

Finally, we have to look at the resolution of the test. Tayor's pH test has color blocks for every .2 change in pH in the K-2006 while the color blocks on test strips are will have a resolution of .4 to .6 which makes it difficult, to say the least, of getting an accurate pH reading.

On 2/22/2021 at 3:22 PM, samwise801 said:

Those strips all say my ph is quite low right now (after adding Dichlor and MPS yesterday, so it makes sense for the ph to be low because the MPS is acidic, correct?), in the range of 6.6-6.7.

Not with a TA of 80-90, that is on the high side for a tub with borate. 50-70 is better for pH stability. If you find that your pH rises quickly then lower the TA. DIchlor is only mildly acidic, MPS a bit more but it is not added as much as a chlorine source unless you are using a silver nitrate cartridge like Nature 2. My question is why you are using MPS? Do you have persistent combined chlorine over 1 ppm? If not it's really not necessary in most cases when doing dichlor/bleach

 

On 2/22/2021 at 3:22 PM, samwise801 said:

I use one of the Aqua Check readers with the TruTest strips, as well as strips from three other companies, and all the others that don't give me a digital reading also return a color hue that says ph is low. 

.You are putting your faith in a $50 photometer to read the strips. Realize that pool store colorimieters that read samples are in the price range of $1000 to $2000 and even those have limitations when compared to a liquid reagent titration for several of the tests. The main reason that pool/spa stores use these readers is that they are very fast and can produce a printout with the associated computer software that some high school kid working part time can hand to a customer with a list of the products they "need" to balance their pool or spa. (I used to work in that side of the industry so I speak from experience). Running tests using a Taylor Waterlab requires more training and actual understanding of pool water chemistry. (I worked in a store that used a colorimeter and sample water added to dry reagents in vials that were then read in the machine. This particular companies system has been upgraded to use disc with several reagents so different tests can be done at once instead of individual vials read separately which saves even more time so more customers can be tested in less time. It's a good system IF you understand the limitations and precision of some of the tests and the interference that affect the results.)

Bottom line, if you want to verify whether the strips or the Taylor are giving you accurate results you can get a bottle of pH standard solution. Taylor has one with a pH value of 7.2 and Granger sells several with various pH for calibrating pH meters. The only one suitable for your test kit and strips would be a pH 7.0 standard. I have tested various kits and strips against standard for pH and some of the other tests and that is why I use Taylor kits.

The ONLY test strips I use are LaMotte borate test strips and Aquachek/Hack salt titrator strips. The LaMotte strips are accurate enough for determining if your borate level is in the 30-50 ppm range. Their advantage over Taylor, Hach, and AaquChek borate strips is that they are MUCH easier to read since their color block go from rose pint to tan. The other strips have very close shads of tan that are next to impossible to differentiate. I have personally checked the Lamotte strips against a standard method boron acid/base titration test with mannitol and they are more than accurate enough for our purposes for spa/pool use. The Salt titrator strips are for salt water chlorine generator systems and are less prone to error for the average user than the silver nitrate/chromate tittraion test for chloride (such at Taylor's salt test kit) since it is easy to go past the endpoint on the titration.

Hope this answers your question. (trust the Taylor, ditch the strips)

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Awesome, thank you for the detailed reply Waterbear. Since I made this post it seems like every time I test the pH with the Taylor kit I'm getting a value of 7.7ish, which is freaking me out 'cause a) the test strips' readings are moving over that same span and b) I'm used to my tub's pH needing adjustment regularly. But it sounds like I need to take a deep breath, trust the Taylor, and remember this is my first refill a) with the Dichlor-then-bleach method, b) with borates in the water, and c) without chasing the 120+ TA that was recommended by the tub's user manual. 

1 hour ago, waterbear said:

DId you let the sample sit to cool down or just keep the tub uncovered and get a new sample when the water had cooled?

Yes, I let the same sample just sit and cool down for a while. It was not a new sample from a cooler tub. 

1 hour ago, waterbear said:

My question is why you are using MPS? Do you have persistent combined chlorine over 1 ppm? If not it's really not necessary in most cases when doing dichlor/bleach

Two reasons:  first, I do have a Nature2 silver ion cartridge in the water, mostly just for insurance / peace of mind in case I'm not perfectly diligent about the FC levels. I figure having Nature2/MPS in the water gives me that extra layer of sanitizer protection and mini-MPS shocks for cleanliness. (I also have an ozone generator, for similar reasons.) And second, the product I have on-hand (bought several bottles of it before the most recent dichlor-bleach refill) is Leisure Time's "Renew," which as I understand it is a combination of MPS and Dichlor. So I'm just using what I have already, really. 

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1 hour ago, samwise801 said:

Two reasons:  first, I do have a Nature2 silver ion cartridge in the water, mostly just for insurance / peace of mind in case I'm not perfectly diligent about the FC levels. I figure having Nature2/MPS in the water gives me that extra layer of sanitizer protection and mini-MPS shocks for cleanliness. (I also have an ozone generator, for similar reasons.)

I am not a fan of N2 for several reasons. However, if you are doing dichlor/bleach and have ozone there is really no need for the N2 as you are trying to combine 2 separate sanitizing methods. Silver/MPS/High water temperature is an EPA approved sanitizing method for hot tubs along with a weekly chlorine shock. As an alternative, N2 and low chlorine can also be run (about a 2 ppm FC level, which is what you will get if you follow the instructions for substituting dichlor after each soak for the MPS as directed in the N2 instruction pamphlet)  However, ozone destroys chlorine and silver on its own is NOT an effective residual sanitizer because it has very slow kill times (particularity against enteric pathogens which are a concern) and is ineffective against viruses.

 

1 hour ago, samwise801 said:

Leisure Time's "Renew," which as I understand it is a combination of MPS and Dichlor.

Renew is MPS, Replenish is a mixture of MPS and Dichlor and personally is a product I would not use. Why would you add chlorine and MPS at the same time? The advantage of MPS is to allow you to enter the water 15 minutes after shocking and to destroy persistent chloramines over 1 ppm that chlorine can't. If you need MPS then use MPS, otherwise, chlorine is a better choice for oxidizing (shocking). IF you are using MPS with N2 and hot water then you want to use MPS and shock with chlorine weekly or more often if needed. There is no reason I can see to combine them.

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1 hour ago, waterbear said:

I am not a fan of N2 for several reasons. However, if you are doing dichlor/bleach and have ozone there is really no need for the N2 as you are trying to combine 2 separate sanitizing methods.

Ah, okay. Why aren't you a fan of N2? Is there a negative to using it? (Aside from the cost of the silver cartridges and the associated MPS.)

1 hour ago, waterbear said:

Renew is MPS, Replenish is a mixture of MPS and Dichlor and personally is a product I would not use. Why would you add chlorine and MPS at the same time?

And yes, my mistake - I'm using Replenish, not Renew. We got started on Replenish when we first got the tub, and our local pool store told us "use the silver cartridge and then put this stuff in at the end of every soak, and you'll be fine." So I get the sense the store was just trying to simplify water maintenance for the newbies, by giving us fewer things to add. 

Now that I've switched to dichlor-then-bleach I'll be buying straight dichlor rather than the Replenish combined stuff once I work through my current stash of Replenish (1.5 bottles left). But you think I should ditch the MPS altogether? And the silver ions? Is it harmful to use them, or is it simply not/just barely helpful? Is there not some utility in having multiple sanitizers in the water, or do they conflict with each other in some way?

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My problem with any type of metal ion system, whether it's a cartridge of silver nitrate or silver/zinc, or an electronic copper/silver or silver/zinc or copper/silver/zinc ionizer, or a "sanitizer" that is basically very expen$ive copper sulfate in either liquid or dry form and often have the word "Blue" in the name along with wording to make you think your water will be "Pristine" or it will be "Clearwater" or some other such nonsense is that they really don't sanitize well. Metal ions have been used in water treatment and they do work but the difference is that there is a holding chamber that allows for a long contact time since metals are slow acting. They are also ineffective against viruses. You can call them minerals if it makes you feel more warm and fuzzy but the bottom line is that you are putting heavy metals into your water. Most governments worldwide have banned the use of ionizers without a primary fact acting residual sanitizer (which means either chlorine or bromine), often at a reduced level. It is interesting that this 'reduced level' of sanitizer has climbed over the years from .5 ppm to about 2 ppm, the reason being that .5 ppm leave nothing in reserve if there is a sanitizer demand. Fun fact #1, every bather will add about 5-10 ml of urine and about 10-25 mg of fecal matter to the water no matter how clean they THINK they are (even if they shower before entering) and in a heated tub every bather will sweat. Fun fact #2, sweat is almost identical chemically to urine. The organic matter (and pathogens) that are added can quickly deplete the small amount of fast acting residual sanitizer leaving only the metals, which take a long time to kill bacteria and have no oxidizing ability. Likewise, sweat and urine will react with and deplete the primary sanitizer and create chloramines (or bromamies) and other volatile oxidation byproducts. the net effect is to leave you with undersantized water.

MPS is a good product when used appropriately and for the right reasons. With silver it becomes a primary sanitizer but only at the elevated temperatures found in a tub. If you run your tub at a lower temperature and bring it up to full temperature before use (which I have seen done) it means that your water is not sanitized while the temperature is low. MPS does have some drawback, the biggest being it is a known sensitizer and many people end up with a contact dermatitis after soaking in a tub that has been oxidized with MPS. Chlorine is NOT a sensitizer. In fact, 'bleach baths' with a FC level up to 50 ppm are used to treat eczema in babies , children,and adults:

https://www.aad.org/public/diseases/eczema/childhood/treating/bleach-bath

https://www.mayoclinic.org/diseases-conditions/atopic-dermatitis-eczema/expert-answers/eczema-bleach-bath/faq-20058413

(Mayo clinic's recommendation of 1/2 cup 6% bleach in 40 US gallons works out to a FC of 48 ppm!)

Hope this answered your questions.

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