One annoying little number...

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The powers that be can not agree ;) ... so the shock levels vary a little as the CYA goes up between the calculator and the chart ... either will work fine, but the chart is a little more aggressive.

Just proves that this is not an exact science experiment.
 
I seem to be the person who keeps having results that defy logic. I swear; I'm not an idiot. This morning my overnight FC had dropped 4... at least that's what I thought. I checked it again immediately and it showed a loss of 2. Thinking that was weird, I immediately checked again. This time no loss. I checked a 4th time...back to a loss of 4! Then I got to remembering, that on every single morning check that I did, the first test always seemed to show an extreme loss (8-9 ppm loss), so I would retest, and the second test would be more reasonable (the 4-6 loss). Then I remembered all of the bizarre readings I have been talking about: the gain in FC after 2 hours of sunlight, the loss of FC after adding bleach. I never retested those incidents. Is it possible that my reagents are bad? I know the first thing everyone is thinking is user error. I can promise you: yes I have read the instructions and watched the videos. Yes, I hold it at eye level and put the bottom of the miniscus at the 10ml mark every time. Yes, I make sure the DPD powder spoon is completely full every time. Yes, I make sure I count the drops carefully, swirl as I go, and am extremely careful when titrating. No, I'm not a moron. I am a college educated teacher with two degrees; one of them in science and I have worked with very precise scientific equipment in professional labs. So I ask you: has anyone else ever experienced this kind of discrepancy with their tests? Was all this shocking perhaps for nothing because of faulty tests?
 
ecowolf said:
I seem to be the person who keeps having results that defy logic. I swear; I'm not an idiot. This morning my overnight FC had dropped 4... at least that's what I thought. I checked it again immediately and it showed a loss of 2. Thinking that was weird, I immediately checked again. This time no loss. I checked a 4th time...back to a loss of 4! Then I got to remembering, that on every single morning check that I did, the first test always seemed to show an extreme loss (8-9 ppm loss), so I would retest, and the second test would be more reasonable (the 4-6 loss). Then I remembered all of the bizarre readings I have been talking about: the gain in FC after 2 hours of sunlight, the loss of FC after adding bleach. I never retested those incidents. Is it possible that my reagents are bad? I know the first thing everyone is thinking is user error. I can promise you: yes I have read the instructions and watched the videos. Yes, I hold it at eye level and put the bottom of the miniscus at the 10ml mark every time. Yes, I make sure the DPD powder spoon is completely full every time. Yes, I make sure I count the drops carefully, swirl as I go, and am extremely careful when titrating. No, I'm not a moron. I am a college educated teacher with two degrees; one of them in science and I have worked with very precise scientific equipment in professional labs. So I ask you: has anyone else ever experienced this kind of discrepancy with their tests? Was all this shocking perhaps for nothing because of faulty tests?
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Well... I won't test unless the pump's been running for half an hour or so, and I usually give it a few passes with the brush to be sure things are mixed well. Also, there should be a few undissolved crystals after you mix the R-0870 or you may get a low reading. Somewhere on this site is a chart that shows the tolerances of the tests. Something like +/-2 drops when you get over 20, but don't quote me on that. The key is, is your water clear? The whole object is to keep the water clear and sanitary, not to have perfect numbers.
 
Richard: The pump has been running 24/7, and yes, the water is clear; cystal clear. It was clear to start with. That's why I asked the forum if I should shock just because of a number. Several people recommended that I shock, so I did. I wasn't seeing this discrepancy when I was testing at lower levels. Does the test perhaps become unreliable above certain numbers? Is it maybe that I'm using a Taylor kit instead of a TF100?
I guess the immediate question though, is: do I continue shocking? I feel like I should let things drop down closer to normal numbers and then do an OCLT, double check all numbers, and decide from there.
 
I think Richard hit the nail on the head. Enough R-0870 powder should be added so that there's always a few or more undissolved crystals on the bottom after adding and giving it swirl. With high Chlorine levels it takes more powder to saturate the pool water solution. The only way to determine this is to make sure there's always some undissolved powder left on the bottom of the vial.
 

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TF100 uses Taylor reagents ... same as the their kits.

You certainly try letting the FC come down given that the water is clear. If you are seeing normal FC losses each day and the CC does not reappear, then you would seem to be fine.

Not really sure how to explain the confusing tests though ... maybe it was the amount of powder you were using as has been suggested?
 
If you are being too careful and taking too much time to do the test, you might be getting the differences from taking too long on the test. I too have seen some differences like you are seeing, but I attribute those errors from going too fast. I have a speedstir and I would add drops a little too fast and didn't get the proper drop size. The drops wouldn't be a consistent size during the test, thus the skewed results.

You might try a OCLT with a lower amount of FC that is around 10 or so to see if this helps.
 
Hmm. All very interesting. I'm surprised no one else has run into this problem. Perhaps it is the amount of powder. I had never heard that I needed to have undissolved crystals on the bottom, meaning, I'm assuming, that the solution you are creating needs to be completely saturated with DPD powder. I certainly didn't even check for that. Could be drop size, also, I guess; when you are putting in almost 50 drops, you can't help but put them in a little fast. I'm going to let things fall back today and try another test tonight at whatever numbers I end up at by the end of the day.

Oh, and just to clarify: There never was any CC. It has always been 0. The reason for shocking was a 1.5 loss of FC overnight.

Thanks again for everyone's help!
 
What I do:

Rinse Chlorine Vial with pool water.
Fill to 10ml mark.
Add a heaping spoon of DPD powder - or MORE if FC is high.
Swirl and check for crystals.
Hold 10ml sample in right hand.
Squeeze out air from the reagent in left hand with bottle tip up.
Start swirling 10ml sample... don't stop for anything.
Invert bottle and start dropping 1 drop every 1/2 second to 1 second.
REMEMBER YOU NEVER STOP SWIRLING AT ALL
Once the sample is clear... KEEP SWIRLING
Add R0003 reagent (5 drops)
IF it turns pink - squeeze out air, invert R0871 bottle and drop some more at the same rate as before
WHILE SWIRLING...

This seems to work for me without any real variation from sample to sample - the results on a daily basis are predictable and repeatable. The extra DPD powder is needed only when FC is higher than normal.
 
Well, perhaps it is user error then. I certainly am at a very high FC level. I have been bumping it to 24 overnight to prevent dropping below 20. I also only put in level spoonfuls (in fact, now that I think about it, maybe less; the little spoon tends to get caked up with dried DPD crystals that are dark grey. I try to clean it out each time by scraping it with a wire, but who knows if I was actually getting an even spoonful.) I also was putting in 10 drops, then swirling, then 5 or so more and swirl, and as I got closer and closer to my expected number, I would swirl after each drop. I'm not sure I'm coordinated enough to swirl and drop the whole time for 50 drops! ;)
This all could be the problem. I think the test at a lower level tonight will tell. I will make sure I have crystals on the bottom and try to swirl the entire time.
 
If your FC is 25, a level spoonful will not be enough...I think you (and others above) have found part of your inconsistency!

ecowolf said:
I'm not sure I'm coordinated enough to swirl and drop the whole time for 50 drops!
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For those of us who are not coordinated enough, or are not blessed with a speedstir, I find that holding the vial bottom on a table and moving it back and forth while adding drops, mixes it well for me. I find that I can't do it in air without sloshing some out sometimes.
 
Too little powder skews the results lower. Taking too long such as swirling 5 seconds or more between each drop skews the results higher especially if you're at shock levels. I don't bother to get that perfect swirl going in the beginning. For instance, if I know that I have at least 5 ppm of Chlorine, I will concentrate on getting 7 distinct droplets of R=0871 in the vial fast and then stop and give it the good swirl. I then slow it up a little and give it that good swirl between each of the 4 or 5 remaining drops.
 
ecowolf said:
Well, perhaps it is user error then. I certainly am at a very high FC level. I have been bumping it to 24 overnight to prevent dropping below 20. I also only put in level spoonfuls (in fact, now that I think about it, maybe less; the little spoon tends to get caked up with dried DPD crystals that are dark grey. I try to clean it out each time by scraping it with a wire, but who knows if I was actually getting an even spoonful.) I also was putting in 10 drops, then swirling, then 5 or so more and swirl, and as I got closer and closer to my expected number, I would swirl after each drop. I'm not sure I'm coordinated enough to swirl and drop the whole time for 50 drops! ;)
This all could be the problem. I think the test at a lower level tonight will tell. I will make sure I have crystals on the bottom and try to swirl the entire time.
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IMHO You need a speed stir! It will help with testing consistency...plus it is a really cool toy. Er I mean piece of essential equipment. :goodjob:
 
Well, looks like not enough powder is looking very suspect! I am still very surprised no one else has run into this problem, especially since my levels are based on a CYA of 50, which granted is at the high end, but still considered "normal".
Hopefully, if this is the solution, someone who reads this can avoid this problem in the future and not waste so much time, reagents, and bleach. I bet I have gone through 10 gallons of bleach and almost two large titration reagent bottles already. I'm sure the shocking was probably a good thing, though. Especially after that massive pool party. :)
 
ecowolf said:
I also only put in level spoonfuls (in fact, now that I think about it, maybe less; the little spoon tends to get caked up with dried DPD crystals that are dark grey. I try to clean it out each time by scraping it with a wire, but who knows if I was actually getting an even spoonful.
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This is easy to fix. Wash it off and dry it out over night. I do that every now and then when it gets too caked.

ecowolf said:
I also was putting in 10 drops, then swirling, then 5 or so more and swirl, and as I got closer and closer to my expected number, I would swirl after each drop. I'm not sure I'm coordinated enough to swirl and drop the whole time for 50 drops! ;)
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I've tried this and I don't think this itself is a major issue. Once you are close - swirl the whole time - but be careful about overshooting.

Speedstir is probably a cool toy - I may get one with refills next year - but I have gotten so coordinated I'm not sure I need it. The CH testing (33-38 drops for me) is the one that wears me out and seems the most sensitive (along with TA) to the speed of the dropping and swirling.
 

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