Question about Taylor K-2006 kit and pH testing

[howardpassman]

I mentioned in another thread that I use a Hanna HI-98128 pH meter, but always use the Taylor K-2006 kit to double check it. I know I'm doing it twice, but I have a reason. One, is I like the second decimal place readout of the Hanna. It doesn't make any difference except I can kind of watch trends a little closer. Second and most important to me is I simply can't see the difference between 7.6 and 8.0 on the Taylor comparator. I've tried every kind of light and every kind of background.

So my question...is there a way, using the R-0005 acid demand reagent, to calculate the actual initial pH reading by starting out with the sample and adding the acid demand reagent until the sample is 7.4 or 7.2 on the comparator? I have no problem discerning those colors.

For example, if I start out with a sample and it's 7.6 or above. If I put one drop of R-0005 in and it falls into the 7.4 range, can I surmise what the actual initial reading was? Another way to put it is, if I do the above, can I calculate, by number of drops of R-0005 used to get to 7.4 on my comparator, the starting pH?

Thanks very much,

Howard

 

[tim5055]

Howard, it does seem to make sense, but chem geek will have to answer that one. He is on several times a day, so,I would expect to see an answer soon.

 

[howardpassman]

Thanks tim5055. I'm trying to back in to the numbers using Taylor's acid demand charts, but I don't trust myself that much, so it would be nice to have someone confirm any findings I make.

Howard

Howard, it does seem to make sense, but chem geek will have to answer that one. He is on several times a day, so,I would expect to see an answer soon.

 

[howardpassman]

I think I'm getting there. Using Taylor's chart for 31.45% Muriatic acid, I looked at the demand for 1 drop of reagent at 20,000 gallons and it came up with 18.4oz of acid. I multiplied the result by .9 since my pool is only 18,000 gallons and that came to 16.5oz. I then used the Pool Calculator and came up with this chart... I'm using the "desired pH" of 7.4 because I can discern that color on my comparator.

actual despH TA acid TA acid TA acid TA acid TA acid
8.00 7.40 120.00 38oz 110 35oz 100 32oz 90 29oz 80 26oz
7.90 7.40 120.00 34oz 110 31oz 100 29oz 90 26oz 80 24oz
7.80 7.40 120.00 30oz 110 27oz 100 25oz 90 23oz 80 21oz
7.70 7.40 120.00 24oz 110 22oz 100 21oz 90 19oz 80 17oz
7.60 7.40 120.00 18oz 110 16oz 100 15oz 90 14oz 80 12oz

So here's an example of how I figure this works. If I have a TA of 100 and it takes 1 drop of R-0005 to bring the color in my comparator to 7.4 then my starting pH must have been about 7.6. If my TA is 100 and it takes 2 drops to bring it to 7.4 on my comparator then my starting pH was 8.0. I see that drops are actually to large of an amount to really make use of this, but it's a start. I may end up having to dilute the drop of R-0005 to get this thing worked out. It seems like a lot of trouble, but if I can't tell the color shifts in the comparator, I can't think of a way around it.

Up for suggestions

Howard

Added: Maybe I could dilute the R-0005 1 to 1 in order to be able to get a little more detail out of the result??

 

[jblizzle]

I don't think you should be mixing methods. The acid demand test takes the TA into account automatically. If you are going to use the demand test, why not just add that amount of acid?

 

[howardpassman]

you would think that if you were dealing with a sane person I'm actually just trying to back in to my pH number because I can't read the comparator above 7.4. I normally like to keep my pH at 7.5 and I have no way of telling if it is 7.5 if it's around 7.6 or up. I guess I could run the acid demand test and then decide not to add acid if it brought it to 7.4, but I'd kind of like to know what it really was to begin with.

Considering that R-0005 is somewhere between .1 and 5% sulfuric acid (according to their MSDS sheet) I guess the demand test doesn't require too much accuracy. They mix sulfuric acid with ionized water, so I'm not sure why I couldn't do the same thing with Muriatic acid or sulfuric acid myself. At this point I'm just experimenting for fun, but I would like a way to get closer to my correct pH reading.

I don't think you should be mixing methods. The acid demand test takes the TA into account automatically. If you are going to use the demand test, why not just add that amount of acid?

 

[chem geek]

So my question...is there a way, using the R-0005 acid demand reagent, to calculate the actual initial pH reading by starting out with the sample and adding the acid demand reagent until the sample is 7.4 or 7.2 on the comparator? I have no problem discerning those colors.

Yes you can do this but it's tricky since you'd need to use my Pool Equations spreadsheet which is not designed for novice users. You could use PoolMath instead, but for pH calculations it isn't accurate enough for what you need. It accounts for TA and borates via some lookup tables but doesn't currently account for CYA which doesn't matter for some ranges but does matter for others.

So the first thing to do is to figure out what those acid/base demand drops are equivalent to so you can know what to put into the spreadsheet for those drops. The base demand drops say that 1 drop is equivalent to 5.13 ounces weight of soda ash in 10,000 gallons while the acid demand drops say that 1 drop is equivalent to 9.16 fluid ounces of 31.45% HCl in 10,000 gallons. So you can use your pool numbers in the spreadsheet, most especially for the TA, CYA and Borates levels, then use 10,000 gallons for the pool size (for simplicity so we can use the numbers I just gave). You most likely will be using the acid demand drops to lower the pH in the tube to the range that you can read more readily.

Let's say you end up with 7.2 and it took 2 drops to get there and your TA is 80 ppm, CYA 50 ppm, and you have no borates. If you put these numbers into the "Initial" column then press the "Reset Goal = Initial" button, now you can play with the Initial pH value until you get 2*9.16 = 18.32 fluid ounces to show up in the Goal column blue area in the Acid section for "Muriatic Acid (fluid oz.)". I get 8.0 as the Initial pH since that gives me 18.5678 that is close enough to 18.32. You can already see one problem with the acid/demand test -- the resolution for the drops is way too large. They are only good for large movements, not small ones. A range of +/- 1/2 drop in this case would imply a volume of 1.5*9.16 = 13.74 to 2.5*9.16 = 22.90 with an implied Initial pH range (using the same example) of 7.79 to 8.22 which is pretty broad.

 

[howardpassman]

Thanks Chemgeek. I'm going to try your Pool Equations spread sheet. I pretty much came up with a similar set of numbers (i had 9.2 oz of muriatic acid). What threw me was Taylor's listing on the reagent R-0005 as >5%. I then looked at the MSDS sheet and it said from .1 to 5% sulfuric acid. That's a pretty big range. With your equivalents maybe I can back in to a percentage.

Anyway, what do you think of taking the reagent and diluting it. I figured by diluting it maybe 16 to 1 I can come up with something resembling a serviceable solution. That would make my calculation for a TA of 100 and a pH of 7.8 take 6 drops in order to get a reading of 7.4 in the comparator. Taylor uses deionized water to dilute their sulfuric acid, but I figure for my purpose I could simply used distilled. What do you think??

 

[chem geek]

Distilled would be fine. It just needs to be unbuffered. 16 to 1 sound more than is needed since you can't read better than around 0.1 in pH units on the comparator anyway. Probably something on the order of 4 to 1 would be enough or perhaps somewhat more.

 

[duraleigh]

Of course, you could just ask someone else to read the pH test for you. Simpler is ALWAYS better.

 

[domct203]

Of course, you could just ask someone else to read the pH test for you. Simpler is ALWAYS better.

+1 Isn't that what TCPC is all about anyway, "simple"?

My 5yo daughter loves to help me take care of the pool. It's her job to tell me what the pH reading is, and count the drops for FC.
Now, if she was just tall enough to vacuum ........

Dom

 

[howardpassman]

because I really didn't know what the percentage of sulfuric acid was in the R-0005 ( backed in to a 1% solution) I tried mixing 3 parts water with 1 part R-0005. I figured that would put me at a good starting point. As fate would have it my pH was reasonable this morning and I could pretty much tell it was around 7.6 on the comparator. I used 1 drop of R-0005 and it came right into the 7.4 reading. Then I took my concoction of 1 to 3 R-0005 and water and tried it. 3 drops did the same thing to a new sample. According to my chart it should have been 2. So that at least puts me in range considering the comparator is in .2 increments and it's still a judgment call. Lamp color temp, background, etc. have got to play heck with reading it anyway.

According to what I figured out it would take 7.75 drops to bring it from a 8.0pH reading down to a 7.4pH with a TA of 100. I probably can't get too many more drops in the comparator anyway, so this should work.

In the end I took a third sample from my pool sample and checked it with my Hannah meter after doing a two point calibration. The meter said the water was 7.52. So I'm a happy camper for now. I'll probably try to refine the process later even though it really doesn't make much difference based on using the comparator.

Thanks once again for your help and input. BTW, that Pool Equations spread sheet is amazing. I'm good with Excel, but obviously not chemistry. Still, that had to be a ton of work. Thanks again.

Howard

Distilled would be fine. It just needs to be unbuffered. 16 to 1 sound more than is needed since you can't read better than around 0.1 in pH units on the comparator anyway. Probably something on the order of 4 to 1 would be enough or perhaps somewhat more.

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What! And leave the house I've been to the pool store exactly twice all year and both times it was for reagent. I'm right outside of D.C. and I wish this traffic on no one.

Have a great weekend!

Of course, you could just ask someone else to read the pH test for you. Simpler is ALWAYS better.

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Sad to say I'm an "Empty Pooler". Kids are grown and gone, but had I known I may have been able to enlist them to help me.............well, between sports and school, I'd still be waiting.

Have a great weekend!

+1 Isn't that what TCPC is all about anyway, "simple"?

My 5yo daughter loves to help me take care of the pool. It's her job to tell me what the pH reading is, and count the drops for FC.
Now, if she was just tall enough to vacuum ........

Dom

 

[chem geek]

BTW, that Pool Equations spread sheet is amazing. I'm good with Excel, but obviously not chemistry. Still, that had to be a ton of work. Thanks again

It was mostly done over a 2-year period working on it every now and then when I got a chance to do so. Yes, it was a lot of work and I was inspired in some of the techniques by some other spreadsheets I saw that some professors had done (with less complex systems). There are programs that calculate chemical equilibrium such as CEA and MINEQL+, but I wanted something that could be given out freely to others if needed and that was portable on PC and Mac.

 

[BuckeyeChris]

If it's somewhere between 7.6 and 8.0, add enough acid until the test is somewhere between 7.0 and 7.4 Is there a compelling reason to be that specific with the pH? I am at risk for scaling and I try to get a good read on my CSI but....my pH is going to keep rising either way, whether I put in 20 oz of 28 oz of muriatic acid isn't going to matter 12 hours from now. Testing that specific is only necessary if your are going to be adjusting your pH every day.

 

[DebbieO]

Jeez, my brain hurts!

 

[chem geek]

If it's somewhere between 7.6 and 8.0, add enough acid until the test is somewhere between 7.0 and 7.4 Is there a compelling reason to be that specific with the pH? I am at risk for scaling and I try to get a good read on my CSI but....my pH is going to keep rising either way, whether I put in 20 oz of 28 oz of muriatic acid isn't going to matter 12 hours from now. Testing that specific is only necessary if your are going to be adjusting your pH every day.

Just note that the rate of carbon dioxide outgassing is faster at lower pH (see this chart) so if you do larger swings then over the long run you will be adding more acid. If you were able to go between 7.8 and 7.6 then there would be less outgassing and less acid usage, but you'd need to add acid more frequently. Using 50 ppm Borates as a non-carbonate pH buffer will slow down the pH rise so that you don't have to add acid as frequently. And of course, the source of the rising pH in the first place is related to the TA which mostly measures bicarbonate in the water. So lowering the TA level should be the first thing to do in a situation with rising pH that is coming from carbon dioxide outgassing.

 

[BuckeyeChris]

I've been at a TA of 80 for a solid 9 months. It's those darn water features

But yes, I see what you're saying, more frequent dosing is less recovery acid so to speak. I also realized this acid from Fry's is only 14.5. I did notice the lack of noxious fumes the last couple boxes. That should have been a clue. I will have to go to the pool store for something....

 

[chem geek]

The half-strength is not bad if you can get it for half the price. Not having as much fuming is a good thing, but it's up to you which you prefer to use.

I don't understand your statement about having the TA be at 80 due to the darn water features. If the source of your pH rise were due to carbon dioxide outgassing, then every time you added acid you would lower both the pH and the TA. The carbon dioxide outgassing only raises the pH with no change in TA. So your TA should have been dropping over time. The only way it wouldn't would be if you had increasing TA from other sources such as evaporation and refill or adding TA raising chemicals (baking soda or washing soda) or if the source of pH rise was not mostly from carbon dioxide outgassing.

Specifically, every cup of full-strength acid (or two cups of half-strength acid) you add to your 10,500 gallon pool should lower the TA by 3 ppm. If that has not been happening, then we need to look for other sources of rising pH (or sources of TA addition that you should stop if possible).

 

[BuckeyeChris]

I meant "it's those darn water features (that keep raising my pH)." The first month of the pool build, 15 months ago, I added some baking soda, but since then it's always been 80.

Plus, perhaps curing plaster. And yes, it evaporates and gets auto refilled from the tap (post water softener). I've never checked the TA of the tap water.

 

[howardpassman]

I can never tell if it's between 7.6 and 8.0 or even higher. If I put in enough to bring it from 8.0 to 7.5 and it's really at 7.6 or 7.8, then I have a bit of a problem, plus I'm lowering my TA unnecessarily. I've worked it out now, so it's quick and easy. If it's 7.6 or above, I start adding drops of my concoction to the sample until it falls to 7.4. Then by number of drops I know almost exactly where my pH is within .1. I do check it everyday. I'm retired and happily puttering around the house and yard.

Howard

If it's somewhere between 7.6 and 8.0, add enough acid until the test is somewhere between 7.0 and 7.4 Is there a compelling reason to be that specific with the pH? I am at risk for scaling and I try to get a good read on my CSI but....my pH is going to keep rising either way, whether I put in 20 oz of 28 oz of muriatic acid isn't going to matter 12 hours from now. Testing that specific is only necessary if your are going to be adjusting your pH every day.

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Ha ha, my brain always hurts...

Jeez, my brain hurts!

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Thanks for the chart chemgeek. BTW, should I be using Borates?? Is there a downside to adding them?

Howard

Just note that the rate of carbon dioxide outgassing is faster at lower pH (see this chart) so if you do larger swings then over the long run you will be adding more acid. If you were able to go between 7.8 and 7.6 then there would be less outgassing and less acid usage, but you'd need to add acid more frequently. Using 50 ppm Borates as a non-carbonate pH buffer will slow down the pH rise so that you don't have to add acid as frequently. And of course, the source of the rising pH in the first place is related to the TA which mostly measures bicarbonate in the water. So lowering the TA level should be the first thing to do in a situation with rising pH that is coming from carbon dioxide outgassing.