Help interpreting FAS-DPD FC/CC test results **Sorry, long, techy post**

[JuJuBee]

Fair warning....this post is very long with details because they are necessary to get the level of help I need right now; to get to the bottom of a very frustrating problem I'm having. I'd appreciate it if anyone would be willing to spend some time going over my numbers and help me figure out what is going on.

Important to note: our pool water is totally clear and has been since April 30th. No algae has been seen in the pool. We only had a cloudy problem with excessivley high pH and Alkalinity >250 in mid-April. After following the advice given here, by the beginning of May our water was, and still is, crystal clear, sparkly and beautiful. There is no visual evidence of any problems whatsoever since May 1st. There is no color other than clear, pretty blue. There is no dirt or silt on the bottom of the pool and we don't leave anything floating on the surface. It's extremely clean. There has been very little swimming in it - no more than 10-15 minutes three times after school and one 30-minute swim for Dad and one son. Our kids are older, not toddlers or little.

I'm trying to get rid of my CC level which has finally decreased to 1.0-2.0 after three weeks but has stuboornly remained in that range for the past six days. In order to make sure my FC is truly reaching it's shock level, that I don't lose more than 1.0 ppm FC overnight, and that my CC reaches .5 ppm or less, I need to be very accurate with my test results using the K2006. I have been having problems with that since I received the test kit the end of April. Wisely, I was advised to set it aside for a while until my CC came down and I could hold a higher FC level....I got there 6 days ago.

This morning, I tested FC and CC against the liquid shock we are using to determine it's true strength; I was beginning to think we were being sold very old and weak chlorine. I used a method AnnaK just shared with me under the post titled, "How to test the liquid shock from pool store for it's available chlorine." My test results for the 12.5% liquid bleach we use returned a solid and confident 12.6 ppm FC and 0 ppm CC. (I know ppm is not the same as %s, but doesn't getting 12.6 ppm just confirm that the 12.5% is still available in that bottle of chlorine?)

But most importantly, for the first time I saw what an accurate test looks like while using the K2006 when all the chlorine is FC; when CC is = 0 ppm.

I have been confused as to "when" I have truly reached an endpoint on either portion of the test with my pool's water because my results don't behave the way the test describes or the way this morning's liquid shock test did; I want to determine if my inability to reach shock level and get rid of my CC after four long weeks is because of this (resulting in adding too little chlorine.) All of my testing for the past 6 days, (regardless if it was 10 ml or 25 ml) have gone something like this:

6 days straight:

FC between 10.0 and 16.5
CC between 1.0 and 2.0
pH 7.5 steadily rose to 7.8 which held for no more than 18 hours
TA between 126 - 155, CYA 60 - 70

aerating pool constantly and running pump constantly
(Using thepoolcalculator.com for calculating amounts)

8:00 pm last night FC 9.0 and CC 1.0, pH 7.8
8:30 pm added 3 gallons 12.5% bleach
9:15 pm FC 16.5 and CC 1.5
9:45 pm added 2 gallons 12.5% bleach

Today
6:40 am (5 gallons of 12.5% bleach later!) FC 12.0 and CC 2.0, pH 7.4!!
7:45 am added 3 gallons 12.5% bleach
8:00 am added 50.5 oz borax
10:45 am (8 gallons of bleach later) FC 12.5 and CC 3.0, pH 7.3!
(my jaw is still on the floor...)
5:45 pm FC 7.5 and CC 1.5, pH 7.2!
I just added 3 more gallons 12.5% bleach and the last of my borax 25.5 oz.

My testing for FC and CC looks like this:

Adding DPD powder to sample for FC test:

First let's compare this morning's successful liquid shock 25ml sample:

Added only 1 scoop of powder and the sample turned vibrant pink the instant the powder hit it. Clear, dark, hot pink. Only required a few swirls....several seconds of swirling unnecessary.

Adding DPD powder to my 10 ml pool water sample

I add 1-2 scoops of powder to get pink. I don't get an immediate pink nor a hot pink. I get a faint, light pink and while swirling the powder for several seconds, it gradually darkens a little bit. It does not reach the vibrant hot pink the way testing the shock this morning immediately did.

Adding drops of R-0871:

Compared to the liquid shock 25ml sample (expecting more drops needed for .2 multiplier):

Every drop added from 1 up to 50 creates no change or disturbance to the color. After 50, the subsequent drops yield only a lighter hot pink. By drop 60 a faint pink appears. Drop 61 it's getting clearer but there is definite color. Drop 62 is the first (AND ONLY) drop I have difficulty determining whether it's truly clear. Uncertain, I add drop 63 and an immediate difference is seen as it is obviously crystal clear now. It holds permanently, no slowly changing into a somewhat dirty or yellowy or foggy clear. (When my pool water testing reaches this "drop point" I could have anywhere from 5 more to 75 more drops with the same behavior as drop 62 did here.)

Adding R-0871 to my 10 ml. pool water sample (expecting less drops for .5 multiplier):

It only takes to the 4th or 5th drop to turn the sample's color from pink. I'm assuming that's respective to a 25ml test's 20th drop or so. The problem is my pool sample doesn't turn to clear but loses it's stronger color and becomes a very faint blush color which didn't happen until drop 60 and 61 in my shock test so I think I must be close to the end. While it's a definite "change" to the color, it is not clear, and after swirling, it darkens again.

I add one subsequent drop at a time and swirl. Each drop behaves the same: Turns the sample clear light pink or light blush, and then slowly returns to a dull cloudy pink.

Usually near the 10th or 12th drop, a new pattern emerges: Each drop turns the sample clear of any color - but cloudy. Then in under 10 seconds of swirling it returns to a dull cloudy light pink.

By the 15th drop, the drops turn the sample perfectly clear as it looked when I poured the sample water initially into the tube. This is when I "re-assume" I'm reaching an endpoint. But, this clear holds for only one to two seconds before a very faint blush, but still clear, starts to return. Each subsequent drop holds the complete clear for a second or so longer than the previous drop, and then it begins to lose it's clarity - and I get confused by what I'm seeing. Once could think it is clear of color because it is so far removed from the initial pink color and side by side you would call it clear. If going at a reasonable pace, you might never have the time to see it changing before adding the reagent for the CC part of the test. But I do and a hue does return that is definitely blush and not "clear" of color. I know this, because one more drop removes that "blush" and returns the water to perfect, crystal clear and it's obvious there was a change. What's not obvious, is whether or not another drop is needed each time. And it's such a borderline decision that that one tester could viably say the end point is reached while another tester might feel they need to continue and does "just one more drop" to see if it changes ... but for several more drops, because it always does.

When I continue, I do so until a drop added turns the sample to resemble what it looked like before the DPD powder was added - a permanent crystal clear and remains that way for a good 30 seconds. But I always begin tracking the total number of drops starting at the point it begins to get difficult to read. If you consider drop 62 of the shock test, which was the first uncertain drop in that test, it required only one more drop to reach and remain crystal clear. But my pool's 25ml water tests always get uncertain by drops 20 thru 30 and my 10ml sample by drop 10 or 11 (when my chlorine is supposedly higher) or by the 6th or 7th drop when it's lower, and both have required 10-20 more drops of uncertainty before a permanent clear is reached.

It "sounds" exactly right, just like the instructions make it sound, to swirl after each drop and make sure you've reached a permanent end point. But it contradicts what the Taylor rep told me in a phone consultation (see conversation below.) And, if this test is suppose to be the most accurate when needing to observe minimal differences of .5 or 1.0 ppm, and provides the convenience of not relying on color comparison for accuracy, then a color-blind, or color-confused, individual would have stopped adding drops in my tests after the 12th - 15th drop, noted the FC to be 6.0 ppm - 7.5 ppm, and continued on to get a bit higher CC reading than mine.

Because I have a really good eye for color changes and differences, including color versus no color, I can see the return of a faint blush and know for certain there will be a very noticable difference when I add another drop of R0871; and I'm proven right when instantly, after adding that drop, there is a definite change to "crystal-clear-of-color." Before that drop, my husband can't tell if it's still clear or not and doesn't know if we should continue; sometimes he's absolutely certain it must be the endpoint. But as soon as I add that drop, he recognizes the obvious change to having no color, ("oh my gosh, you're right, you wouldn't have known if you didn't see that...!") and it remains for a moment before gradually turning again, if it's going to. And this continues on and on. When I finally reach a point where even I can't see a change after say 30 seconds, I record the FC, which usually has been between 12.5 ppm - 16.5 ppm.

You can see how that's a pretty significant difference from 6-7 ppm if you are looking to see if you lost more than 1.0 ppm of FC overnight. The color-blind tester, or a tester who moves along at a reasonable pace, doesn't notice any further change in color and would have recorded an FC loss of 6.0 ppm or greater from the previous night whereas my recorded amount shows just a .5 or 1.0 ppm FC loss from the night before. Always, my CC is either the same as the night before, lower by .5 or 1 ppm or higher by only .5 or 1 ppm.

We've been trying to get our FC to shock level (20, 24 or 28 ppm) for three weeks and have never gotten above 16.5 ppm no matter how much bleach we add. For instance, consider these two days:

7:00 am FC = 6.0 - 9.0, CC = 2.0, pH = 7.5 and CYA = 70

9:00 pm added 3 gals 12.5% bleach 111 oz Borax (1 1/2 bx)

10:00 pm FC = 16.0, pH 7.5
7:00 am FC = 16.0, pH = 7.7 CC = 1.0

7:20 am added 2 gallons of 12.5% bleach (to protect from loss during day)

7:30 pm FC = 11.5 CC=1.0, pH = 7.7

A phone consultation with Taylor was not very helpful. I was given what they considered was a clear cut clarification that really wasn't. As per the rep I spoke with:

Me: Why doesn't it ever stay clear once it loses it's color?
Rep: "If you let it sit too long, it's going to change back to pink because of reacting to the oxygen in the air. But if it starts to return to pink, then you haven't reached your endpoint."
Me: How long is "too long to sit? I mean, how long do I wait to see if it changes and how quickly do I then add the reagent after I see it."
Rep: "Well, a whole minute can be too long."
Me: So, if I see it hold clear for 10 seconds, put it down, go to grab the reagent, and when I'm just about to start to add those drops I notice the color of the sample returned to a faint blush...
Rep: "Then you haven't reached your endpoint."
Me: And if I'm certain I have because it's been about 30 seconds, and I grab the pencil to note the # of drops, grab the reagent to start the CC part and THEN I notice it begin to slowly get cloudy or blushy at what must be close to the 40-45 second point, you're saying that's oxygen?
Rep: "Yes."
Me: So I just add the reagent drops anyway, even though sometimes the sample has returned to a light pink after 60 seconds?
Rep: "Yes."
Me: But when I do that, I get a much higher CC reading - how do I know it's accurate and I wasn't suppose to continue adding drops for the FC part of the test?
Rep: "Then you have a high CC. Look, 60 seconds is a long time. 15-20 seconds is a long time. You can't let it sit that long or it will react with oxygen and always turn back to pink."

That is not how the liquid shock test went down, and it sat for several minutes. After 60 drops, just 2 slowly turned back to blush pink or cloudy blush pink. My pool water tests have upwards of 10 - 50 drops that return to blush in exactly the same way. Since it was the shock test's first two drops to reach almost clear, they didn't take 30 seconds to begin to turn back to a blush, it happened almost immediately. That's the same way the first 2-drops that reach almost clear behave with my pool water test. And when the first drop of the shock test turned the sample completely clear, it remained clear permanently - but it was drop number 63. With my pool water, I could have almost permanent clear on drop 7, drop 10 and 11, then on drop 14 and 15, then drop 18, then drop 23, 24, 25, 26....until the end point is reached. On my 25ml samples, the first clear may not happen until drop 20 or 25, but then I have many more.

I was hoping I could get to the bottom of all of this once and for all. If anyone can help me reconcile the contradictions I experience in this test, I would greatly appreciate it. If I have been doing it wrong by adding too many drops during the FC test and I should stop a lot sooner, I really need to know that at this point because then all my readings are wrong as are my additions of chlorine. What parts am I doing right? What parts am I doing wrong? Why do I sometimes read in other posts a recommendation to let the sample sit for a minute or two before taking the reading?

Thanks so very, very much for your time.

[BigDave]

I'd like to point out that one major difference between your pool water and the bleach sample is the bleach has no CC and your pool clearly does. Perhaps the slow return of pink during the pool water test is some of the CC becoming FC without the reagent you add before the CC test. If this is the case, your CC is realy quite higher than you are presently measuring. I've read many if not all of your posts (and I'm not going to re-read them) and I don't think you've actually gotten your FC to shock level and held it there (if this is wrong, I'm sorry). This could be exacerbating the situation. You keep adding chlorine and producing CC but you never get the level high enough to clear up the CC.

You could test this with a bucket of pool water say about 4 gallons. Add 1/2tsp of your self certified 12.5%. Should bring your FC up about 20ppm. Stir. Measure FC and CC stopping the FC test the first time it goes to clear.

[PoolDoc]

JuJu;

I don't mind your doing this . . . but your post is much too long for the regular forum sections.

And, while we like people to be experimental, since it helps us enlarge our knowledge base, we don't actually like it so much between May 15 and June 15, when we're just slammed. So, please don't be offended if we kinda ignore you for the next month, at least when you're doing stuff like this. Testing chlorine bleach samples is not really central to pool operations. And, if you REALLY want to pursue it, Taylor makes an iodide based test that is for just that purpose.

OK?

[JuJuBee]

I do understand, Ben. Way, way more than you're understanding my intentions in posting.

My "chlorine sample test" is not the main idea of this post, and it was NOT done just out of a general curiosity, but in an effort to eliminate the possibility that I have purchased a bad batch of bleach and therefore have actually been under-chlorinating all the while you have instructed me to reach and maintain shock levels that I can't.

I'm still trying to figure out how to and needed help. Your last post to me was

Hi Judy;
I did a bunch of editing on both yours and my posts, . . .

Let me start by saying as plainly as I can: I don't know -- not for sure -- what's going on with your pool. I think I can guess, but I am not completely certain.

... hand your husband that stupid Taylor book and ask him to hide it somewhere, where you can't find it. You're asking a bunch of questions, because you've read that book carefully...[/I]

"-------------------- In progress -- not finished yet --------------------" (you wrote that...)

that was May 11th . . . and I still haven't figured out how to reach shock levels and see them in my test results. I've been politely patient and tried to find other people to help, I started asking for help early, in April, to AVOID the holiday, I've understood how busy it is, and I didn't blame you for not getting back to me.

I mention the sample test in this post solely to compare it with how I've been using the FAS-DPD to test my pool water as an attempt to "eliminate another possibility of error" which is:

is my testing method flawed so that I am not calculating the right amount of bleach to reach the shock level you told me I needed to get to and stay at to get rid of the CC? If it is, then I can start correcting that.

I seriously don't know what I've done differently from any other poster on this site to have this exchange. I've maintained respect and politeness in every way I could. I've observed and read MANY long, wordy posts by others, in April AND May, yet none of them were handled this way. The only few as long as this one were also technical in nature.

As for your comments just now, I really MUST reply:

JuJu;

I don't mind your doing this . . . but your post is much too long for the regular forum sections.

** I don't know any shorter way to describe how I've been testing so that you guys can best troubleshoot why I can't reach shock levels or reduce CC.

In order to avoid posting long in the wrong sections, I asked first, in a different post, where I should put this and I was told in the testing section.

I created three other short posts to handle other questions. I purposefully did not put them in this post. I kept this post focused on the testing problems I'm having in using the kit.

Please know I am trying my best to be mindful and respectful of the timing of my problems and the length in explaining them. But they are just as valid and important as all the other problems being posted.

And, while we like people to be experimental,

I'm not being experimental at all! I'm trying to solve a very real problem and have been consistently since April 17th!

since it helps us enlarge our knowledge base, we don't actually like it so much between May 15 and June 15, when we're just slammed. So, please don't be offended

but I very much am as I am no different from any other person coming to this forum needing help
... yet I still really like this forum, it's moderators, and all the knowledge and advice.

if we kinda ignore you for the next month, at least when you're doing stuff like this.

"stuff like this"? Because of the holiday, I thought being thorough with my testing problem would SAVE time and not cause dozens of needed back and forth replies asking for all of this exact information and causing your moderators more work. I truly thought I was being thoughtful and making it easier for you to give LESS replies, but MORE educated; thereby actually saving all of us time.

This post had to focus on more techy stuff, so I kept it's focus just that. It was necessary to receive help in my use of the FAS-DPD and reading the results correctly. I've seen many other loooooong posts on the specifics and usually Chem Geek or Waterbear chimes in. I just assumed this one post would be read by them being that it's more technically detailed.

Testing chlorine bleach samples is not really central to pool operations. And, if you REALLY want to pursue it, Taylor makes an iodide based test that is for just that purpose.

I don't really want to pursue testing chlorine bleach samples. I kept THAT one in a very short post, received immediate and perfect help from AnnaK, and moved on.

I'm so confused over why I've been misunderstood all this time. Maybe it's just time to set intolerance aside and thoroughly read my posts?

I sound upset, but please know I sincerely feel all this is a big misunderstanding and if you had the time to truly look closely at my posts, you'd realize that. I don't think you mean to upset me at all and I still am not displeased with any of you. I know you don't want this site to be "intolerant" and I do hope we work this out and find a way to understand each other better.

OK?

[JuJuBee]

Thank you so much Big Dave! You are exactly right, I have NOT reached shock level once, not once, in spite of all the chlorine I have used. This link shows my most recent attempts to do just that: http://www.flickr.com/photos/50351313@N03/7260036226/

Thank you for giving me something to try to get a clearer test result. I'll follow it and post the results as soon as I can.

[BigDave]

JJB,
Did you read my post, just beore PD's? Do you think that answers or helps lead to an answer to your long post from last night? I interpret your long post to be asking( in a very detailed way) "Why does my FAS-DPD testing work differently than it seems it should?"

-- OOPS -- so you did.

Take it easy, see if you can clear up the CC in a bucket, then you'll know you can clear your pool.

[chem geek]

Do you have a pool cover that is dark or opaque? If so, uncover your pool at least part of the day to let sunlight on it as that can help bring down the CC.

I don't know why the FAS-DPD chlorine test isn't giving you clear readings. Though sometimes the water gets a little cloudy during the test, the color transition is usually pretty clean. See this link and click on "Pool/Spa" on the left, select the K-2006 "To Test (Free and Combined Chlorine) using FAS-DPD".

By any chance was your pool converted from a different type of sanitation such as Baquacil/biguanide/PHMB? There may be something in your pool causing interference with the FAS-DPD test.

[JimK]

....Adding DPD powder to my 10 ml pool water sample

I add 1-2 scoops of powder to get pink. I don't get an immediate pink nor a hot pink. I get a faint, light pink and while swirling the powder for several seconds, it gradually darkens a little bit. It does not reach the vibrant hot pink the way testing the shock this morning immediately did.

......

This part caught my attention. Are you adding 2 scoops of DPD powder to the water sample per Taylor's instructions? This part of you post sounds like you are adding 1 (incorrect) or 2 (correct) scoops.

I'm not sure why your sample would return to pink after turning clear. I've been using this test kit for years and it has never behaved that way. One possibility I just thought of is that it will return to pink if the DPD powder hadn't completely dissolved before adding the reagent (it will return to pink as the remaining powder dissolves).

[waterbear]

I am a bit confused why you are constantly aerating and why you keep adding borax when your pH has not tested too low. What else are you trying to accomplish besides eliminating CC? What you describe is symptomatic of a very high CC and low CC. Have you tested your water for ammonia and have you tested it with OTO and if you have what color did the OTO test turn?

[waterbear]

This part caught my attention. Are you adding 2 scoops of DPD powder to the water sample per Taylor's instructions? This part of you post sounds like you are adding 1 (incorrect) or 2 (correct) scoops.

I'm not sure why your sample would return to pink after turning clear. I've been using this test kit for years and it has never behaved that way. One possibility I just thought of is that it will return to pink if the DPD powder hadn't completely dissolved before adding the reagent (it will return to pink as the remaining powder dissolves).

The amount of DPD powder is not critical as long as the pink color forms. If you are using a 10 ml sample one scoop is more than sufficient and often is with a 24 ml sample also.

If there is very high CC it is common for the color to return to pink on FC part of the test. The sample will also return to pink if allowed to stand. This is normal behavior.

Also, the pink will not return if all the DPD has not dissolved since there would be no more chlorene for it to react with once the titration is complete.