First Test with TF-Pro and bizarre FC readings?

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Deb04 said:
In the first post you said that CYA is > 80. If it is > 80, your SLAM target is higher than 31. If it’s >80, but 90 or less, target is 35. If it’s >90, you need to do a diluted CYA test.
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CYA is still a crazy hard test to read! I think my >80 was off as I brought the tube too close to my eyes. I did it again the next day and didn't outside at waist level and it looked closer to between 70 and 80. Hence the 80 value for SLAM
 
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longinoa said:
> For extremely high FC levels, you can use 5ml sample water and 5ml chlorine-free water (e.g. distilled water); then each drop of R-0871 counts 1ppm FC/CC. This can save on test reagent.
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It will work either way, I just use the 5ml. Adding 5ml of water, I believe, just adds another potential for error. I'll talk with Allen, and we may update the wiki...
 
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Okay I must be very dense...

2 hrs ago I tested FC (10ml pool water) and got 27.5.

Added enough to get to 31.

Just tested with 5ml and got 41.
Tested again with 10ml and got 30.

The 2 things that likely impact this
- ability to accurately measure 5 or 10 ml.
- ability to accurately drop in.

Is there a good video on adding the reagent? Because I'm likely doing that wrong
 
Do you have a speed stir?

Evacuate a bit of air before inverting the bottle.
Hold the bottle vertical.
Squeeze VERY slowly. Allow the drops to form and drop under their own weight. Think oooooone oooone Thouuuuusand drop. Twwwwwo ooooone Thouuuuusand drop.
Doing this will allow the drops to fully form. Squeezing them out quickly allows the drops to be undersized and you will get a higher number and variability.

Also remember the test is accurate +/-1 drop for each 10 drops. That is assuming that you have consistent drop sizes. With inconsistent drop sizes, your error goes up.
 
PoolStored said:
Do you have a speed stir?

Evacuate a bit of air before inverting the bottle.
Hold the bottle vertical.
Squeeze VERY slowly. Allow the drops to form and drop under their own weight. Think oooooone oooone Thouuuuusand drop. Twwwwwo ooooone Thouuuuusand drop.
Doing this will allow the drops to fully form. Squeezing them out quickly allows the drops to be undersized and you will get a higher number and variability.

Also remember the test is accurate +/-1 drop for each 10 drops. That is assuming that you have consistent drop sizes. With inconsistent drop sizes, your error goes up.
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speed stir yes - and I am doing consistent about 1/second

The error of +/-1 drop for 10 helps ground things I am just dealing with such a high number of drops due to high CYA - once I finally pass my OCLT and get done with this numbers will go down and Ill stop having so many drops!
 
As @DrewLG said, a .5ml error on filling 5mL will be a 10% error. Being .5mL off on a 10mL sample will be 5%. Using the 5ml introduces more potential for error.
 
@PoolStored I really appreciate your help! trying to get all this under control has been a fun exercise! I have a science background (albeit not chem) so understanding where errors come in and how to reduce them really helps ground things for me
 

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SLAM finally ended! OCLT came back at 1ppm lost!

Water looks great (more sparkling than I've seen since we moved in).

Used just over 17 gallons of chlorine, a bottle and a half of the fas/dpd reagent and nearly an entire thing of the powder.

I asked for quotes for a SWG (not sure if I want to DIY)

And finally - I fired my pool company today!


Thanks for all the help!
 
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I actually am pretty sure I slammed for 2 extra days - my OCLT the 2 previous days were 1.5ppm off but the error margin at 31ppm FC is pretty high.

I now have a samplesizer which vastly helps the water measurement
 
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