Testing FC before and during slamming

[ictshocker]

New pool owner (came with the house). I'm not totally sure what I am missing here, but hoping someone can help.

Using the Taylor K-2006 kit. Testing Chlorine using FAS-DPD method (and watched video on how to do it).

Testing using the .2 ppm method for sampling. When I add R-0870, I cannot get the water to go beyond barely pink, not matter how much of the powder I add. When watching the video, after only two scoops the water turns bright pink. Will also say the powder does not seem to want to dissolve very easily and seemed kind of clumpy in the container. Could I have a bad test kit?

Anyway, after just one drop of of R-0871, the water turned from the very faint pink to clear. After about 20 seconds though it would begin to turn VERY faint pink again. So another drop and it would turn clear, then 20 second later, faint pink.. and so on (always turned faint pink slowly)

Also, based upon my current CYA level (40), I have a target FC of 16 during the SLAM process. How do I test for chlorine levels that high? If my math is correct, for the the .2 testing I'd expect to use 80 drops during the test! I'll run out of testing agent pretty quickly at this pace...

Help?

Thanks!

 

[ship of fools]

Use the .5 testing instead. Your other issue is a lack of chlorine. You have almost none in your pool


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[ictshocker]

Thanks! Was wondering about that. Amazing that i have so little considering how much i added over the last week prior to starting the slam process.

Using store bought "shock" treatments, I guess I wasn't giving it enough to overpower everything that was in my pool? So I never built a reserve?

 

[Texas Splash]

Now you can see the advantages of being in control of your water with the proper test kit. Amazing we ever tried before without them right?

 

[ictshocker]

Right! One more question... two days prior to SLAM I showed a CYA of 45, removed some water and refilled. CYA came down to 40, so I thought I was in a good position to begin the SLAM (started yesterday). I've gotten my FC up to the target of 16 (for about 18hrs now) using 8.25% bleach. So far so good. But just did a CYA test again and now show over a reading of over 90! Does the SLAM affect the CYA reading?

- - - Updated - - -

As additional FYI, after initial 320 oz. of bleach yesterday evening. Tested this morning and I was at 11% FC. Added another 120 oz this morning and about 60 again this evening and am hanging in right at about 16 FC. Does it seem like chlorine is being consumed a too high a rate? I'd think if my CYA was as high as my reading showed just now (over 90), my FC would be drawn down VERY slowly (and its been a cloudy day here today)?

 

[Texas Splash]

It sounds as if there may have been a mistake in your second CYA test. No way the results could change like that, and the SLAM should not have any effect on CYA. You might want to double-check your CYA testing and check back in with us if you need a little help.

 

[ictshocker]

Will do... curious, is it correct that if my CYA were really that high, I'd see much slower rate of depletion for FC?

 

[Texas Splash]

Here's a good thread on that subject from one of our resident experts: what's so bad about high CYA levels?

 

[rmturner54]

How concerned should she be with the cya level once the slam is started?

 

[duraleigh]

How concerned should she be with the cya level once the slam is started?

That's a really good question. The answer is absolutely not at all.

There is nothing in the SLAM process that will change the CYA in your pool.....nothing. So, if you start a SLAM with 40 ppm, you can be assured your CYA value will be 40 ppm both during and after the SLAM.

Another way to think off it is that you are getting your chemistry correct before the SLAM...

pH - around 7.4 or so...CHECK!

CYA - 30-40 is ideal....CHECK

FC TC CH and TA - All CHECK

Takeoff! Run the SLAM the way it is supposed to be done and your only testing should be the FAS/DPD test keeping the FC at the SLAM value you have chosen.

When the SLAM is Complete and you have passed the OCLT, Take another set of tests to prove to yourself just how smart you really are and then settle down with a cold one!

 

[ictshocker]

Okay tested CYA and FC again today (had a pretty heavy rain last night so had to drain some water). As expected with the rain, FC dropped from 16 yesterday evening to 11 around noon today.

CYA dropped from almost 90 yesterday to around 80 today. Made sure I was testing properly. Still cannot figure how how I went from readings of 45 and 40 CYA prior to SLAM to 90 yesterday and 80 today (guessing the addition of rain water brought it down a bit).

The only thing I did when it was at 40 prior to slamming was add water because it was a bit low. Would it matter that I added water from our well as opposed to treated city water? On a 32x16 pool at 3.5 feet deep, I'd say I added only an inch or so.

Now unsure if I should stop slamming altogether until I get my CYA back down, which I understand involves draining and adding water. But if adding water is what's increasing CYA, hesitant to do that as well...

I'm stumped....

Thanks!

 

[tim5055]

Adding water will not increase CYA level. It is not anything you will find in either well water or city water. You have to add it.

It's up to you as to weather to drain/refill to get the CYA lower or increase the amount of chlorine to attain your "new" shock level.

 

[sbcpool]

I have noticed that high levels of FC can affect the CYA readings, but make them appear lower than they really are. Did you have high FC when you did the first test, or perhaps grab a sample near where you just added bleach?

 

[tim5055]

I have noticed that high levels of FC can affect the CYA readings, but make them appear lower than they really are. Did you have high FC when you did the first test, or perhaps grab a sample near where you just added bleach?

High FC should not affect the CYA test. The only things really known to affect the test is water colder than 70 degrees (let it warm up to room temperature) and extremely cloudy water (very rare)

 

[sbcpool]

While keeping my water at 15 - 20 mg/L FC my CYA tests repeatedly read under 20, but read 40 for weeks prior. No water changes or rain involved.

 

[JoyfulNoise]

While keeping my water at 15 - 20 mg/L FC my CYA tests repeatedly read under 20, but read 40 for weeks prior. No water changes or rain involved.

You can read this thread where we had a very long and detailed conversation about interferences in the CYA test.

The short answer is this - in normal pool water conditions, including those during a SLAM, the CYA test is not affected by FC. The only way to interfere with the CYA test is to have some extremely abnormal water conditions (extremely high pH & FC at the same time that would be well above the testable limits, off the chart CC's, etc).

The CYA test is very subjective and easy to get the wrong read on if the lighting is bad. I have found the best way to do the test is to perform it three times (reuse the same solution) and then average the numbers and round to the nearest tens. You can also get a 50ppm CYA standard solution (from TFTestKits.net) and use that to calibrate your test procedure (find the best location, lighting and eye to tube distance) so that the dot disappears at the 50ppm mark.

 

[sbcpool]

The short answer is this - in normal pool water conditions, including those during a SLAM, the CYA test is not affected by FC. The only way to interfere with the CYA test is to have some extremely abnormal water conditions (extremely high pH & FC at the same time that would be well above the testable limits, off the chart CC's, etc).

As stated by chemgeek in the linked thread:

The more likely interfering reaction would be if the FC level were quite high in which case the chlorine combined with CYA may interfere with precipitating with the melamine where in the worst case the CYA may be underestimated by as much as the FC level.

The CYA test is very subjective and easy to get the wrong read on if the lighting is bad.

People say that, but I find that visible vs. not visible is distinctly NOT subjective. There is no such thing as partially invisible. The black dot is either visible or not. It's binary, unlike most of the color-based tests.

 

[JoyfulNoise]

Yes, but you failed to read the more detailed answer from @chemgeek in this part of thread -

The precipitate of melamine with cyanuric acid depends on hydrogen bonding so doesn't work (or work as strongly) with other forms such as cyanurate ion (3 different chemical species) or the chlorinated cyanurates (6 different chemical species). This is why at normal pool pH melamine cyanurate is soluble to around 20 ppm. The bonding is weak so really depends more on how much CYA itself is present though there is some balancing from equilibrium, but not complete as it is in other tests like the FC test that measures all the chlorine species (i.e. uses HOCl up from hypochlorite ion and the chlorinated cyanurates). This is why the melamine solution in the Taylor test has pH buffers at rather low pH. They are designed to force most of the CYA to be cyanuric acid itself and not have much of the deprotonated cyanurate ion species.

The melamine reagent is designed to buffer the pH of the test solution to a lower pH where the interference caused by high FC are less likely to affect the test. Therefore, as I stated, you would need some extremely strange water conditions (very high pH) such that the melamine reagent failed to shift the pH to a lower value.

As for the subjective nature of the test, I agree that the dot is either there or not there, but the point at which it disappears can easily be affected by poor lighting conditions. This is one reason why the stated tolerance of the test is so large, +/- 10-15ppm at best.

 

[sbcpool]

The melamine reagent is designed to buffer the pH of the test solution to a lower pH where the interference caused by high FC are less likely to affect the test. Therefore, as I stated, you would need some extremely strange water conditions (very high pH) such that the melamine reagent failed to shift the pH to a lower value.

That may be my case as I'm having trouble getting the pH below 8.2, even with a TA of 100. I add a gallon of HCl and two days later we're back at 8.2+.

As for the subjective nature of the test, I agree that the dot is either there or not there, but the point at which it disappears can easily be affected by poor lighting conditions. This is one reason why the stated tolerance of the test is so large, +/- 10-15ppm at best.

As long as the lighting is the same for all of the tests, it shouldn't matter too much. I always stand in the shade of the patio and hold the vial at waist level. When I think the dot isn't visible I shift the tube a little to see if I can detect the dot moving. If I can then it hasn't really disappeared and I keep going until I can't see it move.

 

[JoyfulNoise]

I don't know enough detail regarding the pH buffering of the R-0013 reagent to know how your high pH water will affect the results but perhaps if you post a question in the Chemistry 201 forum, ChemGeek can help you figure it out.


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