Is it normal to see huge swings in FC/CC?

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Butterfly said:
Would you give us a walk-thru on how you are doing the FAS/DPD test?
Some folks have been known to use 25ml water and test as 10ml. Don't ask me how I know this :oops:
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I take my 'chlorine only' tube pool side, stick it in the water upside down with my arm in up to my elbow, invert it to fill, and then take it out. Then I dump out enough until I get to 10ml. I'm careful to fill only to 10ml. Maybe I'm +- 1ml sometimes. Who knows?

I take sample in my house. Put in a rounded scoop of the powder and swirl over some white paper until almost all of the powder is dissolved. I then hold the R-0871 dropper over the test tube and GENTLY squeeze until drops start coming out, about 1 per second. As soon as the solution goes clear, I stop. I cap the bottle. Then I reach for the R-0003. Sometimes by the time I record, grab and uncap the R-0003 and get ready to add it, the solution turns slightly back to pink. Is this the problem? If it turns back to pink, should I go back to adding R-0871 and continue with the FC test? Or is it safe to start adding R-0003 and then test for CC (same method as above)?
 
Casey said:
Maybeeeeee.... the pool isn't as big as what the paper work says it is? Could it be? If you are over shooting the chlorine, it could be possible. Yes? :scratch:
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Could be off a little. But I've measured it myself....if it is off it is not off by much.

I measure 18' x 41'...about 8' in deep end, 3.5' in shallow, rectangular. Pool calculator confirms 27500 is close enough for hand grenades and free chlorine.
 
brian4110 said:
Would that cause the huge swings? I would think ammonia might be the cause of the huge CC numbers I sometimes get, but I have no idea why my FC goes through the roof sometimes after I add a poolcalculator appropriate amount of bleach. I have a hard time believing I am screwing up the testing so badly.
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If bacteria converted some or all of the CYA into ammonia, then when you add chlorine to the pool it will combine with the ammonia in seconds to a couple of minutes (depending on CYA level and mixing) to form monochloramine which will register as CC in the test. Now if the bacteria only partially converted the CYA so that it was partly broken down, then it might take longer for the chlorine to react with it. In that case, you might initially measure FC after adding the chlorine, but over some number of hours the FC will drop and the CC will rise. That looks like what you have been seeing. You need to continue to add chlorine until it holds as FC. It's also possible for algae to slowly consume FC (as they get killed) and form CC, but not usually in the amounts you are seeing.

You can do a bucket test full of pool water and add chlorine to it if you want a rough idea of how much chlorine it is going to take in total until the FC holds (you need to scale amounts, obviously). If the amount of chlorine it will take is huge, then you might consider some water dilution as another option.
 
chem geek said:
brian4110 said:
Would that cause the huge swings? I would think ammonia might be the cause of the huge CC numbers I sometimes get, but I have no idea why my FC goes through the roof sometimes after I add a poolcalculator appropriate amount of bleach. I have a hard time believing I am screwing up the testing so badly.
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If bacteria converted some or all of the CYA into ammonia, then when you add chlorine to the pool it will combine with the ammonia in seconds to a couple of minutes (depending on CYA level and mixing) to form monochloramine which will register as CC in the test. Now if the bacteria only partially converted the CYA so that it was partly broken down, then it might take longer for the chlorine to react with it. In that case, you might initially measure FC after adding the chlorine, but over some number of hours the FC will drop and the CC will rise. That looks like what you have been seeing. You need to continue to add chlorine until it holds as FC. It's also possible for algae to slowly consume FC (as they get killed) and form CC, but not usually in the amounts you are seeing.

You can do a bucket test full of pool water and add chlorine to it if you want a rough idea of how much chlorine it is going to take in total until the FC holds (you need to scale amounts, obviously). If the amount of chlorine it will take is huge, then you might consider some water dilution as another option.
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Thanks. I don't seem to lose FC that fast, honestly. I understand the high CC, or at least I can come up with a scenario that explains it (as you posted above!) But it's the way the FC seems to skyrocket an hour or 2 after I add chlorine that has me puzzled. And I never test less than an hour after I put chlorine into the pool. Should be well mixed by then...and I test from the same spot every time.
 
I take my 'chlorine only' tube pool side, stick it in the water upside down with my arm in up to my elbow, invert it to fill, and then take it out. Then I dump out enough until I get to 10ml. I'm careful to fill only to 10ml. Maybe I'm +- 1ml sometimes. Who knows?

I take sample in my house. Put in a rounded scoop of the powder and swirl over some white paper until almost all of the powder is dissolved. I then hold the R-0871 dropper over the test tube and GENTLY squeeze until drops start coming out, about 1 per second. As soon as the solution goes clear, I stop. I cap the bottle. Then I reach for the R-0003. Sometimes by the time I record, grab and uncap the R-0003 and get ready to add it, the solution turns slightly back to pink. Is this the problem? If it turns back to pink, should I go back to adding R-0871 and continue with the FC test? Or is it safe to start adding R-0003 and then test for CC (same method as above)?[/quote]

Here's the quote from Extended Test Kit Directions:
If left sitting on the counter, the sample will turn pink again one or two minutes after the test is completed. This is normal.
When measuring high FC levels, or measuring FC when the CC level is relatively high, it is important to move through the test quickly. Drops should be added about once per second, or slightly faster, swirling the entire time. You can slow down a little at the end of the test, to give you time to watch for the end point.
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It turns pink again in a matter of seconds, not 1-2 minutes. And I've never restarted the FCC test once I reach for the r-0003. I go into the cc test. I wonder if that is why I sometimes see very big cc? My FCC test wasn't done yet?
 
brian4110 said:
It turns pink again in a matter of seconds, not 1-2 minutes. And I've never restarted the FCC test once I reach for the r-0003. I go into the cc test. I wonder if that is why I sometimes see very big cc? My FCC test wasn't done yet?
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Yep, sounds like. Follow linen's suggestion and add more powder.
 

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linen said:
I would try more of the powder so that the pink is more vibrant...someone has called it barbie pink...so that you can discern the change to clear more "sharply".
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This was my thought as well when reading through the thread. Often there are a couple crystals that do not fully dissolve if you have enough powder from the start. Make sure you have a nice bright pink before you start ... the SpeedStir will help a lot as well.
 
My magnetic stir came in the mail today...just ran 3 tests. All water pulled from same location in pool at same exact time.

Test #1 (manual shake and swirl method...did not use magnetic stir):
FC=7.5
CC=20

Test #2 (magnetic stir used. also used 2 scoops of R-0870 instead of 1):
FC=13
CC=7.5

Test #3 (magnetic stir used. used 1 very rounded scoop of R-0870):
FC=7.5
CC=15

So, when I used 2 scoops, I got double the FC. Maybe I need to use 2 scoops all the time? My CC is all over the map though.

I took a video of test #3. I will try to post to youtube. I'm hoping I can link to the video here and you can tell me what I'm doing wrong. It's a good example of the solution turning clear for 10 seconds, then tinting slightly back to pink. This time I went back to the R-0871 until the clear held for several seconds.
 
Pool pics, as requested...the water seems to be shading more to the blue, less to the green today. Might be the sky or the evening light. Just my impression that is it less mint green and more turquoise today.

It is clear enough that you can easily see the algae/sediment that settled over the course of the day in the deep end on one of these pictures. That's the main drain of course.

You can also see how bleached the liner is...I inherited that unfortunately.
 

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Just tested again (11:30pm) after brushing and got the following:

FC=18
CC=5



FYI, I used 2 scoops of R-0870.

Keep in mind I did NOT add any chlorine or anything else to the water all day! Yet my numbers are all over the map!

So my last 4 results (first 3 tests were taken at same time)...

FC= 7.5, 13, 7.5, 18
CC= 20, 7.5, 15, 5

Without adding chlorine, my FC has more then doubled. I'm quite frustrated now. I don't know how I can follow the shock process when I don't know how to monitor how much chlorine is in the water. Shock level for my CYA is 11. I have no idea if I should add chlorine or not. (I guess I shouldn't, just to be safe because my last test shows me to be above mustard algae level already.) I think my test method is fine because I get consistent results from my TA and CH tests. I don't seem to have any problem there. I'm burning through reagent because I am testing 2 or 3 times every time I test just to verify the result...and the results I get make absolutely no sense.
 
I am not positive, but I think it is likely you have not been using enough of the powder. You inconsistent results are consistent with that being your problem. Even having undissolved chunks in the solution does not guarantee you have enough that was able to go into solution. The R-0870 can get clumpy, and sometimes those clumps will not break up.
 
linen said:
I am not positive, but I think it is likely you have not been using enough of the powder. You inconsistent results are consistent with that being your problem. Even having undissolved chunks in the solution does not guarantee you have enough that was able to go into solution. The R-0870 can get clumpy, and sometimes those clumps will not break up.
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I'm not dismissing that as a possibility. However, I've done 2 tests using 2 scoops of powder today. The first test came out with FC=13. 3 hours later I tested again (2 large scoops) and got FC=18 and I didn't add any bleach at all in between tests.

Interesting that the 2 tests I did today with only 1 heaping scoop both came out with FC=7.5. Might very well be a coincidence (and both those tests came out with very high CC.)

If I'm not using enough powder, would I likely read FC too low and CC too high?
 
If you watch the video I linked, you'll see an example of the solution going to clear and then back to pink before I can add the R-0003 reagent. Is that a symptom of too little powder? The video I posted was one of the tests with only 1 scoop.
 

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