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# Total Dissolved Solids (TDS) Chemistry

• Rating: 5 after 4 votes

﻿﻿﻿﻿﻿﻿Just how much do swimming pool chemicals add to the total dissolved solids (TDS) content of the water? Do all chemicals of equal amounts (by weight) add identical amounts of TDS to swimming pool water?

When one pound of a chemical is added to 20,000 gallons of water, the usual amount of TDS being added to the water is 6 parts per million (ppm) of TDS. While this is true with most chemicals, it is not true with all chemicals. After being added, some chemicals will escape from the water and not contribute to TDS. Another possibility is that portions of some chemicals will convert into water and thus will no longer be part of TDS.

We will first look at adding a pure chemical that provides the full increase of its weight to the total dissolved solids content of the water. Chlorine gas is a good example. At levels of 1000 parts per million or below, chlorine gas is nearly 100 percent soluble at a pH of 5.0 or above. Therefore, if one pound of pure chlorine is dissolved into 20,000 gallons of water, the result will be 6 ppm of chloride (which is TDS).

One way of calculating this is as follows: 20,000 gallons of water weighs about 166,700 pounds, which is one-sixth of a million. Multiply the one pound of chlorine by six to get the 6 ppm of TDS.

As with all acidic sanitizers, after chlorine gas is added, it is usually necessary to add sodium carbonate (soda ash) or sodium bicarbonate (bicarb) to adjust the pH and alkalinity upward. Interestingly however, adding these alkaline chemicals does not ultimately add the full amount of TDS per pound added.

When soda ash and bicarb are added to pools, these chemicals will react with acid that has been added to form carbon dioxide, which, over a period of time, will release into the atmosphere. Only the sodium element from these two chemicals remains in the water and increases the TDS.

The following equations will help illustrate:
Na2CO3 + 2HCl = 2NaCl + H2CO3
H2CO3 = CO2 + H2O

In the first reaction, soda ash (Na2CO3) reacts with acid (HCl) from acidic sanitizers, muriatic acid, or dry acid, to form sodium chloride (NaCl) and carbonic acid (H2CO3). Sodium chloride remains in the water as salt, which does contribute to TDS, while carbonic acid will dissociate into carbon dioxide (CO2) and water (H2O).
The pure water that is formed does not contribute to TDS, and carbon dioxide will eventually escape into the atmosphere – thereby not contributing to the TDS content. Sodium bicarbonate also reacts with acid and forms the same compounds – salt and carbonic acid.

To determine the actual amount of TDS that is being added by these chemicals, a look at their molecular weight is needed. The (rounded off) molecular weight of soda ash is 106, and sodium bicarbonate is 84. Sodium by itself has a molecular weight of 23, and there are two sodium molecules in soda ash, only one in sodium bicarbonate. The sodium element (which adds to the TDS content) comprises about 43.4 percent of the soda ash, and about 27.4 percent of the sodium bicarbonate. Therefore, when adding one pound of soda ash, only 43.4 percent would contribute to TDS, and with sodium bicarbonate, 27.4 percent contributes to TDS.

The calculations are as follows: if one full pound of a material in 20,000 gallons of water would normally equate to 6 ppm of TDS, then one pound of soda ash, with only 43.4 percent of its total weight (sodium) remains as TDS, contributes about 2.6 ppm of TDS. Likewise, one pound of sodium bicarbonate (with 27.4 percent as sodium) adds about 1.65 ppm. (Note: Until these chemicals actually react with an acid, the entire contents of the various compounds would be present as TDS).

Another type of chemical which does not introduce the full TDS of its weight are compounds which adds hydroxide or which forms hydroxide when added to water. Hydroxide (OH) will likely combine with a hydrogen ion to form pure water (H2O) and no longer be TDS. Sodium hypochlorite (often referred to as liquid chlorine or bleach) is an example of this type of compound.

With 10 % (weight) bleach, about 10.5 ppm is added, and with 5.5% (weight) household bleach, about 5 ppm TDS is added, per gallon to 20,000 gallons of water.

Also, chemicals that include oxygen or nitrogen will also likely lose portion of their weight, thus a lower overall TDS contribution. Calcium hypochlorite (65%) is an example of a compound that adds oxygen. The percentage of the calcium hypochlorite contribution that ends up as oxygen is about 22 percent. Cal Hypo also contains a small amount of water. Therefore, its contribution to TDS is only about 75 percent of its total weight. Lower strength Cal Hypo will result in a slightly lower percentage of TDS contribution per pound. (Of course, part of the TDS contributed by calcium hypochlorite is calcium, which is added to the water and increases the hardness).

Trichlor, sodium dichlor, cyanuric acid, and regular salt, added to swimming pool water will result in the full increase of their weight to TDS.

Muriatic acid (hydrochloric acid) is product that, when added to pool water, will contribute significantly to the TDS content. Muriatic Acid at 31.45 percent strength adds about 3 pounds of TDS per gallon. Although the hydrogen from this acid will react with hydroxide to form water, it is such a small percentage of the total weight of the acid that it will not significantly effect the contribution of this acid to TDS. Therefore, one gallon of muriatic acid in 20,000 gallons of water will increase the TDS 18 ppm.

It is recognized that this information on TDS isn’t critical to the understanding and maintenance of water balance, but perhaps some will find it interesting.

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Tags: TDS, balance, chemistry, dissolved, solids, water

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Comment by Clemente Rivera on January 7, 2011 at 9:50am

On another note:

On Mr. Faulk's comment about nitrates and phosphates and algae growth...I once ran into a pool that was completely green from algae, with a phosphate level above 2.0 ppm.  the chlorine levels were over 10ppm, but the pool was still green; also, no CYA was present.  I added an emergency dose of phosphate remover, and in 24 hours, the algae was gone.  How did so much algae get there...Lets just say that somones "propietary scale inhibitor" was the culprit.  Not mentioning which system it was, but Al and I have had a few laughs on that one.

Lamotte specifies a high limit of 1.0ppm for phosphates.

Just wanted to put that out there.

Comment by Clemente Rivera on January 7, 2011 at 9:44am

Hi Everyone:

While TDS has been a stickler for Pool Operators concern for many years, I have recently decided to look at a solution for the Pool Dumping Problem in the United States.  Did you know that states such as New Jersey, and parts of New York State require a pool be dumped at least SIX TIMES PER YEAR!!!.  Suffolk County, NY actually requests a timetable from CPO's every year...

I firmly believe that TDS is not a factor to be concerned about, as I have worked on pools that have fill water with 4000ppm TDS, and have been able to keep them running VERY well.  The issue is whats in the water, as what was previously mentioned.

back to the TDS issue with respects to dumping...I find that this REQUIREMENT to dump millions of gallons of water is attrocious, so I recently started to have a look at what can be done about it.

The answer: RO (Reverse Osmosis Filtration).

I am working on a Utility Patent to create a Service that can come to a Facility, connect to the circlulation system, and reduce the TDS of the pool via a portable RO system (it fits in a semi truck, so its not a small device).  After about 12 hours, the TDS can be reduced to as low as 200PPM (which means you will have to re-balance your pool).  There is still a 25% loss of pool water from the process, but dumping 1/4th of the pool is better than the entire thing.  Also, the service would only be needed when the pool reaches a specified limit 9some codes want pools dumped at 2000ppm TDS, for example).

Im working out some of the issues that arise with RO, especially the issue with the superconcentrated flush water that will be expelled into waste (the EPA restricts how much TDS can be present in that waste - an issue that industrial processes go through every day), but Im finding that there is a comprimise on the horizon.

Just wanted to let you know what people in the industry are doing to solve these operational concerns.

Comment by Richard A. Falk on December 24, 2010 at 11:30pm

Merry Christmas to all as well.

Good info Al.  There is very little that is black and white with pool systems.  There are pros and cons with all, but full disclosure and discussion isn't usually done (unfortunately).

My only counter-comment to what you wrote is with respect to nitrate levels and algae growth.  There isn't a magic number where either phosphates or nitrates get to a point where you can't kill algae with chlorine alone.  Even with plentiful nutrients, algae growth is still limited by sunlight and temperature -- under ideal conditions with only sunlight at its normal limit and at an ideal temperature for maximum growth, algae only double in population in 3-8 hours.  They simply won't grow any faster than that no matter how many nutrients you give to them -- they can only photosynthesize so fast and only reproduce so quickly.

Now it is true that at high phosphate and nitrate levels you really need to stay on top of the sanitizer level because letting it get too low results in a big jump in chlorine demand and ultimately (if chlorine levels continue to get lower) to dull, cloudy, and then green water in a full bloom.  I've had 3000+ ppb phosphate levels in my own pool and can attest to this, but maintaining the appropriate minimum FC/CYA ratio had no unusual chlorine demand nor no other signs of algae in the pool.  The same is true for many other pool owners where high phosphates and/or nitrates were measured.  This is why I say that phosphate removers should be seen in the same vein as algaecides in that they take the edge off of rapid algae growth so are like insurance, but are not necessary if one maintains the appropriate chlorine level relative to CYA.

Comment by Al Neumann on December 24, 2010 at 8:13pm

Merry Christmas Guys.

Just waiting for Santa to come. But while I’m waiting, I might as well put my 2 cents in here now.

I think maybe some clarification is needed on the nitrate/nitrite issue, and why I asked the question on if anyone knew if swimming pools per se, had a recommended maximum level, and if so, what effects are likely to be seen with levles that were considered high. It was initially asked as a TDS type of question, in that I saw a potential for build-ups in some pools, and was wondering what the over-all effect of that would be.

Now I did not expect nitrates to be a health issue in swimming pools, as they are in drinking water for children under 6 months of age due to “blue baby syndrome”. I did suspect there would be some issue with chlorine demand for couple of reasons, as it is well doc**ented as being linked to algae growth due to nitrates being part of its food chain, similar to phosphorus. As Richard stated, nitrates are algae food. A link for the algae connection, and for one of the reasons for chlorine demand, is found here. It also states a limit of 25 ppm’s, although, I don’t yet know where that is coming from. At least it is a start.

As I stated before, the other factor of chlorine demand was what Chip Blatchley found out in one of his studies which showed, and I’ll quote what I wrote before so you won’t have to look back,

“Reason why I ask this is that in one of Chip Blatchley’s papers on DPB’s and UV, he mentions a sort of “nitrogen cycle”, (my words) with medium pressure UV. It appears that the photolysis of chloramines end up as nitrites and nitrates. When nitrates pass though the UV chamber,  exposed to wavelengths under 240 nm, converts the nitrate to nitrite. In pools with residual chlorine, this nitrite is then converted back to nitrate. It becomes a source of chlorine demand not really thought of before, and is a continous cycle. It keeps on repeating, with nitrates increasing by chloramines and I suppose some other DPB’s. Was wondering what effect nitrirates has on the pool, at what levels are a concern, etc. I should note that this is just a concern with medium pressure UV, as low pressure UV  has only the wavelength of 254nm”.

Medium pressure Uvc created a chlorine demand issue by the repetitive conversion of nitrates to nitrites, whch are then oxidized by chlorine back into nitrates. Constantly repeating, constantly increasing in numbers due to the the continued photolysis of new chloramines added by bather load, (which is a good thing). Since, in a way it is like cyanuric acid, in that build-ups can only be reduced by drain and fills, or by RO treatments, then it would be nice to know when enough is enough.

Now do I think that this newly recognized form of chlorine demand is significant. I don’t know, but it may be fuel to feed the controversy between Low Pressure and Medium Pressure UVc manufacturers are going through these days.  MP claims as being far superior to LP technology is not as strong as it used to be. Does the nitrate /nitrite issue play a role in their repective role on chlorine savings claims? Would be nice to know. This particular study by Chip Bl;atchley has been out for a couple of years now, yet no one has talked about it. Kind of wondering why.

My thoughts, as good as MP is, it appears it is not living up to all the exagerated claims that many of their manufacturers/dealers like to make. Like any other technology, it’s a tool to be carefully used. It’s not the panacea that our industry is trying to make it. There are trade-off differences besides the initial cost, and maintenance costs associated with bulb replacement and electrical usage. All you have to do is take a closer look at some of Blatchley’s studies to see that the 99% reductions in chloramines and DBP’s, without any detrimental side effects, isn’t quite substantiated.  You will find that they do quite a good job on some, but also in the process, creates some DBP’s all their own, that are just as bad…yet nobody talks about it. Why??

My apologies to Kim, in that I didn't intend to make this a commentary on UV. This thread is on TDS. And please, don't get me wrong. I'm not against UV. I just like to know the good along with the bad. All technologies have trade-offs. I try to be objective, in my journey in gaining knowledge, and in how I re-act with my customers. I just feel it is up to me, along with my customers, as to decide which trade-offs are acceptable, and which ones are not.

Comment by Richard A. Falk on December 24, 2010 at 12:56pm
Nitrates are far more innocuous than nitrites.  You won't find nitrites in a chlorinated pool since the chlorine will oxidize them to nitrate.  The EPA maximum contaminant level (MCL) for nitrate in drinking water is 10 mg/L (ppm).  The EPA Integrated Risk Information System (IRIS) describes how this limit was set based on the effects of higher nitrates levels in infant formulas.  People do not normally drink large quantities of pool water so the risk is much lower.  This link gives more info on nitrates and nitrites where there is no information on dermal absorption of nitrate.
Comment by David Rockwell on December 24, 2010 at 12:05pm
I've got some test kits to buy. I can see that now. Question re nitrates / nitrites. I remember something about starting up my salt water fish tank that the nitrate - nitrite cycle had to be established before adding fish. Are nitrates in a pool more harmful than nitrites?
Comment by Al Neumann on December 20, 2010 at 6:44pm

Richard,

Thanks for the responce on the nitrate issue. Just a curiosity for me at this point. I know that drinking water has a limit of 10 ppm's, but that's for pregnant women I think. Thought there might be an upper limit of ?? in pools.

You are correct on Taylors pH formulations were compensated to read correctly  up to 10 ppm of FC., not the 25 ppm I stated. Irregardless, we are consistantly seeing some bleaching of the sample at FC levels of less than 3 ppm's, far below the 10 ppm limit. This is using ther FAS for chlorine, and the larger comparator. Not sure if LaMotte has the same issues. Just compared it with Palintest Photometer and a calibrated meter. The simple test is do take any pool sample and test it with chlorine, and then repeat the test without the chlorine. Both pieces of test equipment shjould come up with very close results for BOTH scenarios. If they don't, then what does that mean to you?

As for the CC test and the 2 min wait, I'll email you the standard along with some other info. I don't know how to do an attachment here. Seems to me that if we are going to do DPD testing, then we should be following the standards that were developed for this test, and not just some made up ones. Again, I'll ask the question...If I'm right on this, what does that mean to you? Am I the only one that sees a potential problem with this?

Comment by Richard A. Falk on December 20, 2010 at 1:20pm

Al,

I don't have an answer for you as to what level of nitrates starts to become a problem nor what the problems are at high nitrate levels except some generic ones.  Phosphates and nitrates are essential nutrients for algae so a pool higher in both of these nutrients will have the capacity for faster algae growth.  Nevertheless, such growth rates are ultimately limited by sunlight and temperature so that chlorine alone can still prevent algae growth regardless of these nutrient levels.  I am not aware of specific issues of high nitrates with regards to pool surfaces or equipment or to bathers.

As far as the Taylor pH test is concerned, I find that the inexpensive kits, the 1000 series, have a hard-to-read pH test where the comparator colors don't seem quite right (too red in most I've seen) while the more expensive kits, the 2000 series (such as the 2006 with its FAS-DPD chlorine test), have a larger comparator tube, more intense (saturated) phenol red coloration, and more accurate colors.  As for pH accuracy when FC is present, I did some tests on this since I had asked Taylor quite a while ago about why they didn't need to add sodium thiosulfate drops to neutralize chlorine as some other test kits required.  They said that they had chlorine neutralizers built into their phenol red solution and that sodium thiosulfate itself can affect the pH so the chlorine neutralizers they used were a proprietary combination that limited such effects.  They said that their pH test should be able to read correctly up to around 10 ppm FC (not 25 ppm FC -- no way) though this depended on the TA level, among other things (i.e. if the TA is low, then the pH is more affected by chlorine neutralizer due to less pH buffering in the sample -- technically, borates and CYA would also be factors as they also buffer pH).

I then did some experiments with pH testing using a Taylor kit as well as a Lamotte kit I had where I took water samples and added chlorine to them at different levels.  You need to realize that because chlorine consumption is acidic, that the pH will change at different levels of FC.  When using a hypochlorite source of chlorine, the pH rises when chlorine is added and it drops when chlorine is consumed.  The pH test should measure the pH that existed when the chlorine was still present so any chlorine neutralizing should be designed to not affect the pH.  Though the Lamotte was slightly different than the Taylor (by < 0.2), it was consistent at different FC levels in my tests (all <= 10 ppm FC).

An example of varying pH with FC, in a pool with 100 ppm TA (and 30 ppm CYA and no borates), adding 5 ppm FC raises the pH from 7.5 to 7.7 while adding 10 ppm FC raises the pH to 8.0.  Normally, the reactions with thiosulfate result in the pH rising as the primary reaction not only reduces hypochlorous acid (which would be an acidic process), but also produces hydroxide ion (which is a strongly basic process).

A properly calibrated pH meter would be the best arbiter to determining the true pH.  There are pool owners that have electronic pH meters and Taylor kits and haven't reported seeing such discrepancies but the number of such users is small and their electronic meters relatively inexpensive.  Though I didn't see the "too high" result you have seen, I certainly believe that you saw it.  However, it doesn't sound like it's consistent and I don't know why.  Perhaps some batches of the phenol red solution do not have the chlorine neutralizers being effective -- perhaps they break down over time or are affected by the environment (temperature, sunlight, etc.).  That's just speculation on my part.

As for the Combined Chlorine (CC) test, see this Hach doc**ent that describes chlorine testing in more technical detail.  There is some amount of bleed-through of monochloramines into the Free Chlorine (FC) test so it is best not to wait too long when doing that test or else one can get a falsely high FC reading and a falsely low CC reading.  We've seen this effect when pool owners have done testing of high FC levels in shocked pools where the FAS-DPD is done too slowly (because of so many drops), but we're talking more than a minute or two before such interference becomes significant enough to affect measurement.  What you are describing is the opposite where adding the potassium iodide reagent and measuring too quickly results in missing measuring some of the CC.  This makes sense in that some CC may react somewhat slowly with potassium iodide to form iodine, but I dispute that this error is primarily missing dichloramine and nitrogen trichloride.  Nitrogen trichloride is very irritating and noticeable at even 20 ppb (0.02 ppm) and in practice is usually only seen at measurable levels in conditions such as Blatchley's urea experiments that have >10x amounts compared to pool water (with few exceptions).  Even dichloramine, as shown in Figure 2 in Blatchley's "Volatile disinfection by-product analysis from chlorinated indoor swimming pools" and the corresponding supplement to that paper is < 0.2 ppm in pool samples.  The worst case from all measurements in all pools was a single measurement max of 0.417 ppm for dichloramine in pool #7 (which had monochloramine of 1.09 ppm) and 3.412 ppm for nitrogen trichloride in one single measurement max in pool #9 (which had monochloramine of 0.969 ppm), but those were single measurement anomalies whereas averages were generally far lower.  Also, the CC measurement was generally a lot higher than the MIMS measurements of inorganic chloramines implying that the bulk of CC was something else, probably the organic chloramine monochlorourea, based on Blatchley's most recent paper on urea oxidation by chlorine.

Richard

Comment by Al Neumann on December 20, 2010 at 10:47am
Kim,
Hawaii was great. Thanks for asking. Highlight was jumping off the South Point Cliff’s.
I totally agree with your frustration that the process of going deeper into a subject opens up a cavern of questions that you never knew existed before. Some of us are willing to just stand up on top of that cavern, and are complacent in just looking down, often thinking they have learned enough, or perhaps are maybe just fearful in asking a potential dumb question, or more likely, don’t see a real need in rocking a boat that may affect there bottom line. Problem solving has evolved more into the use of band-aids, rather than truly finding a means of eliminating the source of a problem altogether.
Then there are those that look at that cavern as an adventure, and are intrigue by the journey. The frustration for me is not necessarily the details I don’t understand, as I think that’s part of the journey. What does frustrate me is the general lack of interest our community exhibits in the pursuit of validating scientific claims vs generalizations and myths. Like you said, the deeper you get into something, the more likely something else doesn’t make sense. Our industry is getting much more technical, and some of us are finding out that doing what we did in the past doesn’t necessarily make it right for us to continue to do the same thing now.
Just because some industry puts out a claim, doesn’t necessarily make it true. Case in point, the plaster industry, the water testing industry, and more recently, the UVc industry. None of them like to be questioned. And because these are powerful industries, funding is often lacking in getting any real answers to questions that may make a difference.

So the frustration for me, is in the not knowing where to turn for the science needed to prove or disprove the things that don’t make sense to me. I’ve often been accused by some manufacturers and dealers of asking questions that nobody else has ever asked, and that no one has any answers for. It’s not because they are frivolous questions, it’s because they have the attitude that there’s not enough people asking, so why bother. It’s not to their benefit to pursue answers to questions that for many don’t need answers.

Excuse me for getting a little off topic on TDS, but I’ll try to give you a personal example of this, and explain the way HCF Venturi Liquid Chlorine Feeders are changing the norms in how our pools should/could be fed. We’re doing things with these feeders that are unheard of, and doing so very successfully without overshoots. Feeder sizing has always been controlled by the overshoot dilemma as being the controlling factor. We’ve all, “been there, done that”…with oversize feeders. But what if we could control the overshoot? What really causes the overshoot? What if…

One of the answers that I found, on my own, is in how we program the controller. I give you this example because we had little help from manufacturers on this because no one else had ever asked why this was necessary before. Here’s what we do: We run 2-decimal place pH control, (7.45), with a 0.05 high pH alarm, (7.50), with a 0.04 hysterisis. What that means is that our pH set point is set to 7.45. When the pH goes to 7.46, it proportionally feeds CO2 at a very high rate. When it drops to 7.44, it turns off the CO2. Now, IF the controller gets to 7.50, then it shuts off the chlorine feed until the pH is once again back down to 7.45. One would think that we would be constantly dealing with high alarms, yet… if we ever get a high alarm, its because the CO2 tank is empty. Most of the time, pH never gets above 7.47 as a high, and is often done feeding in 3 cycles. The result is that we are feeding chlorine and CO2 fast enough to meet any demand in minutes, and doing so without overshoots.

So why are we doing this? One of the primary questions that should be asked is why feeders are sized the way they are. The limiting factor has always been the overshoot. If we can overcome this, then the question becomes…Does meeting demand in what really is a timely fashion pre-empt many of the issues we face in dealing with our pools? The answer is maybe. If nothing else, it becomes an important weapon to add to our arsenal to help fight the battles that we all face today. It becomes a 1st step approach. What a concept…meeting demand in what really is a timely fashion.

So, one of the tools we use of increasing the pool's reaction time is simply using 2 decimal place pH control. Why? How many controller manufacturers offer or even recommend 2 decimal place control? Not many offer it, and none actually recommend it. Most controllers “see” and control to 5+ digits anyway. It’s not because we need the precision. It’s because 2-decimal pH control offers a dramatic increase in the SPEED in the pool’s reaction time. It’s this reaction time that controls how much chemical is actually being fed into the pool. It takes far less time to drop from 7.46 to 7.45 than it does for 7.6 to drop to 7.5

The point of all this is there just aren’t very many venues that pertain to answering many of the questions, and very few have thus been answered. We’re more interested in reacting to problem, and offering band-aids as solutions, rather than finding out the real cause of a particular problem in the first place. That’s my real frustration. Which is why I find the discussions between you and Richard so refreshing. Why do you think none of the other highly respected individuals are participating in yor discussions?
Comment by Al Neumann on December 20, 2010 at 10:38am
Richard,
Thanks for the attempt at answering my question on nitrates. I think though that maybe you may have mis-understood my question.I wasn't looking for an amount of chlorine demand that results from the "nitrogen cycle" caused by medium pressure UVc, but more in whether you knew what are considered as being high levels of nitrates, and what effect those high levels would have on the pool or patrons using the pool...aka similiar to TDS, or sulfates, or high pH etc.

There are test kits available for nitrate testing. One that we use, and incorporate as part of our feeder package is the Palintest 25 Photometer, Here

Water testing is wh*** different discussion. It’s amazing how often the Taylor ph test is so far off from the real pH. It’s supposed to be compensated for for up to 25 ppm’s of free chlorine, but really isn’t. Even with as little as 2 ppm’s of FC using the FAS kit, we’ve seen pools controlled and tested with the the Taylor as being 7.5, but were really 7.9. More often it is 0.2 pH units different. Simple test to do. Take a sample and test it with the Taylor, a Palintest 25, and a recently calibrated electronic meter. The Palintest and electronc meter will be real close, the Taylor will be off due to bleaching. Leave the sample sit for 3 or 4 days to get rid of the chlorine. All 3 will be very close. The difference is there is no chlorine to bleach the sample, so there is no bleaching going on.

Another issue with the Taylors, LaMottes, etc is the way they do the Combined Chlorine test. The real parameter by the EPA for the test is to wait 2 minutes after adding the #3 reagent , but Taylor etc, says to proceed immediately. Doing so immediately reads the monochloramines, none of the dichloramines, and ½ of the trichloramines. Waiting the 2 minutes allows a more accurate reading, which is ususally about 2 times the result given with the Taylor. So a 0.4 ppm with the Taylor FAS is realy close to 0.8 ppm. Big difference. Taylor says that they agree that the 2 minute wait is indeed in the EPA instructions, and they will look into it. That’s been close to 2 years ago. Their claim has always been that air oxidation is causing an interference in the test…reason why the sample turns pink again. Yet, nothing changes.

Side note: Chip Blatchley is also showing us that even this may not be all that accurate, as many of the organo-chloramines, (DPB’s), exhibit an interference with the FAS test, so waiting 2 minutes may in fact increase the effect. So maybe reading immediately may somewhat compensate for this. Who knows??? Interesting questions none the less.

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