chlorine test ? - confused

[spf30]

Ok, as per instructed last time, I've brought my CYA of 0 to now what seems to be around 35 and I dropped my pH to around 7.2 (it was high as is TA, but have not rechecked TA as I haven't addressed that issue yet). I have however had to add way more chlorine than was suggested by posters (using calculator) in order to get any reading that would stick. Today, I was able to turn the water from pink to clear (using TF kit) with the addition of 6 drops, (making it 3ppm correct?). However, before I could even add the additional reagents to see if it would turn pink again, the sample turned pink again on it's own! What does this mean?? And I would also like to clarify please...when the water does turn pink, it's not a very dark pink but a pale pink, is that correct?

Also,when using the quick check vial for Cl, how long does one have to take the reading? I was having a hard time discerning the shade of yellow (very pale), so I was holding it up at various angles (with white background), when it seemed the color grew deeper. Does the reading need to take place quickly for results to be accurate? Since I couldn't get a good reading, I went to the FAS DPD test which is when I got the 3ppm. I'm confused as if there were in fact 3ppm, wouldn't that have registered as a much darker shade on the vial?

Btw, water temp is only 66 degrees, and clear, so I don't think there's an algae problem.

Thanks!

22, 000 gal, vinyl lined...

 

[PaulR]

Today, I was able to turn the water from pink to clear (using TF kit) with the addition of 6 drops, (making it 3ppm correct?).

Yes, with a 10ml sample, 6 drops = 3ppm.

However, before I could even add the additional reagents to see if it would turn pink again, the sample turned pink again on it's own! What does this mean??

Nothing. Don't worry about it.

And I would also like to clarify please...when the water does turn pink, it's not a very dark pink but a pale pink, is that correct?

For low FC levels, yes, it will be paler.

Also,when using the quick check vial for Cl, how long does one have to take the reading? I was having a hard time discerning the shade of yellow (very pale), so I was holding it up at various angles (with white background), when it seemed the color grew deeper. Does the reading need to take place quickly for results to be accurate?

The perceived saturation (pale v. dark) will depend on lighting and what you have behind it. The test is intended to be used in natural indirect light (outdoors in the shade, or a room with plenty of natural light). That said, lots of people have trouble distinguishing the degrees of yellow, me included; the "2" and "3" blocks look identical to me.

Since I couldn't get a good reading, I went to the FAS DPD test which is when I got the 3ppm. I'm confused as if there were in fact 3ppm, wouldn't that have registered as a much darker shade on the vial?

You would think so. But I gave up; I don't use the OTO test at all any more.
--paulr

 

[spf30]

Thank you PaulR. I do have a follow up however. You said the clear going to pink on its own is nothing to worry about. Does this then mean I have no CC? Otherwise, how can I get an accurate reading? If adding the reagent to get it to turn back to pink indicates the presence of CC's, and it does it on it's own...how can I tell if I have any?

 

[JohnT]

Are you thoroughly swirling the sample after adding the drops? Often, on the next to last drop, the sample will clear, then turn pink after swirling. Mine always turns pink after standing several minutes, since I only test for CC if I have reason to suspect I might have some.

The OTO test works better in a slightly shaded spot with a white background.

 

[frustratedpoolmom]

Thank you PaulR. I do have a follow up however. You said the clear going to pink on its own is nothing to worry about. Does this then mean I have no CC? Otherwise, how can I get an accurate reading? If adding the reagent to get it to turn back to pink indicates the presence of CC's, and it does it on it's own...how can I tell if I have any?

The difference will be more dramatic. If you add the reagent to check for CC it will turn back to the original shade of pink, not pale. I don't like the OTO either, can't differentiate between 3 and 5 at all. I usually just use the FAS-DPD.

 

[JasonLion]

It sounds like you have/had some ammonia in the pool water. Ammonia can build up in a pool closed for the winter when the FC level falls to zero. Ammonia is most commonly associated with losing CYA over the winter. If you do have ammonia, it will consume a lot of chlorine right at first and lead to a fairly high CC level. You should shock your pool until the FC level holds and the CC is down to 0.5 or lower.

On the FAS-DPD chlorine test, if it turns pink again within about 10 seconds then you need to add another drop. If it takes more then a minute to turn pink then you are waiting to long before testing CC. You need to do the entire test fairly quickly, not racing around but not with any unnecessary pauses either. Long pauses during the test can throw off the results and cause the solution to turn pink again at the wrong time.

You should start the FAS-DPD test with a rich obvious pink, which then fades as you add drops. Then, if there is any CC, when you add the R-0003 to test CC it will turn a reasonably obvious pink again.

On the OTO test, at first the OTO test will read FC and then after a short delay it will start to transition to showing TC. So, yes it is quite possible for the color to change. People who are very good at distinguishing shades of yellow really quickly can use the OTO test to measure FC and TC, but most of us will have trouble doing that and should just wait till the color settles down and use that as the TC reading. The one thing you can reliably distinguish is that when you see the color shifting you know you have CC, even if it is tricky to be sure just how much CC you have.

 

[PaulR]

On the FAS-DPD chlorine test, if it turns pink again within about 10 seconds then you need to add another drop.

Okay, that's news to me.

You should start the FAS-DPD test with a rich obvious pink, which then fades as you add drops. Then, if there is any CC, when you add the R-0003 to test CC it will turn a reasonably obvious pink again.

The initial pink-ness is clearly a function of the FC level; if your FC is feeble, like in the 1-2 range, the pink will be obviously paler than if you're up at 5 or more. (And if it's 0, you get no pink at all...) Same deal with the CC after adding R-0003; with CC in the 0.5 range, it'll be a pretty faint pink. It is sometimes not obvious looking down into the tube but I can tell if I look sideways through the tube.
--paulr

 

[Guest]

However, before I could even add the additional reagents to see if it would turn pink again, the sample turned pink again on it's own! What does this mean??
Usually an indicator of lots of CC or possibly ammonia in the water.

Also,when using the quick check vial for Cl, how long does one have to take the reading? I was having a hard time discerning the shade of yellow (very pale), so I was holding it up at various angles (with white background), when it seemed the color grew deeper. Does the reading need to take place quickly for results to be accurate?
No, actually, this test should be read after a few mnutes to get an accurate reading. The color darkening with time indicates a high level of CC or ammonia.b This test is TC whihc is a combination of your FC and your CC.


Since I couldn't get a good reading, I went to the FAS DPD test which is when I got the 3ppm. I'm confused as if there were in fact 3ppm, wouldn't that have registered as a much darker shade on the vial?
how dark the color is depends on how much DPD powder you add. Did you complete the next part of the test for CC? This test is not a color matching test and how deep the color turns is NOT important. Titrating to endpoint and counting the drops correctly is.

Btw, water temp is only 66 degrees, and clear, so I don't think there's an algae problem.

Thanks!

22, 000 gal, vinyl lined...

 

[PaulR]

Since I couldn't get a good reading, I went to the FAS DPD test which is when I got the 3ppm. I'm confused as if there were in fact 3ppm, wouldn't that have registered as a much darker shade on the vial?
how dark the color is depends on how much DPD powder you add. Did you complete the next part of the test for CC? This test is not a color matching test and how deep the color turns is NOT important. Titrating to endpoint and counting the drops correctly is.

I think spf30 meant, wouldn't that have registered as a much darker shade on the vial for the OTO test.
--paulr

 

[spf30]

I'm sorry for all the questions, but I'm even more confused! It's been 30 years since Chem class..

I'm dumping more bleach and will closely watch levels and add accordingly. Some suggested it may be ammonia, others CC. However, I'm still confused by the tests! In OT(?) test, you add the 5 drops then mix. This measures total Cl correct? So if it's extremely pale yellow, this would either mean there is either little FC, and no CC, or no FC and only CC correct? So it would seem that if I had a very pale yellow and there is no FC in water and it's only CC, then wouldn't it only be a small amount of CC or wouldn't it register as a deeper yellow? So that would mean I could just be shocking to get FC up but not have to be watching any CC levels at this time, or am I way off base here? I know the FAS is more accurate for CC but I don't want to waste it if in fact the OT is not indicating a CC problem (very pale yellow).

And I'm sure this goes without saying, but please say it anyway! I'm trying to get the temp up with a solar cover, however, while I'm nuking the pool, I assume I should leave the cover off???

Thanks!

 

[duraleigh]

I seem to remember that Ben or someone said to use OTO to test for the presence of chlorine.....not much else.

Use the FAS/DPD to test for exactly how much chlorine you have and to test for CC's as well.

That makes sense to me and it is the way I use the two tests.

Emphasizing what waterbear said about the FAS/DPD, it is not the intensity of the pinkish color that counts but, rather, how many drops it takes to clear the pink.

 

[JasonLion]

If the OTO test is very pale yellow and stays that way for a while (more than a minute) then TC is low. That means that FC and CC must also both be low. But you can't say anything about what the distribution between FC and CC is.

In normal day to day usage, you can figure that CC will be zero, and use the OTO test. But when you are shocking, CC might be zero or it might not be zero, and that makes a difference. So you almost always have to use the FAS-DPD test when shocking.

 

[spf30]

Thank you! That's what I was trying to understand. And am I correct in thinking I should not have the solar cover on during the major chlorine 'nuking'?

 

[PaulR]

If you have more CC than you want, leaving the cover off will help get rid of the CC because more sunlight will reach the water.

Also I hear high chlorine levels will degrade the cover faster than usual, so you'd have to replace it sooner.
--paulr

 

[frustratedpoolmom]

Paul is right about the sunlight helping destroy CC.

I will chime in and say I leave my solar cover on while at shock level and have seen no degredation at all. I will shock my pool when I go on vacation and leave the cover on to help cut down on evaporation and FC loss. That is the only time I have to shock, (that and at closing).

For now, while you are trying to rid the CC, leave it off.

BTW, ammonia will read as CC on the tests. Confusing, I know.