CYA testing troubles, R-7065 black dot disappears at 40 ppm.

[Traciecmom]

Just received my TF-100 kit yesterday & the CYA test is giving me trouble. I have tried three different times & the closest reading for the R-7065 sample was 40ppm. When I tested my own water, the dot was visible until about 25ppm. I reviewed recent pool store results & they say my CYA is @ 50!?
I think I may have some algae growing on the wall in the shallow end (although my water remains clear thus far) There is a patch of dark brown/green dots no bigger than a pencil points. They feel slightly slimy at first but do not brush off or scratch off with finger nail!
I am not sure where to begin.??( Especially since I can not figure out how to get an accurate CYA test. )

Here are the rest of my results:
FC 1.5
CC .5
TC 2
PH 6.8
CH 425
TA 50
CYA 25???

About three weeks ago we did an ascorbic acid treatment to remove metal stains. I added Polyquat 60 while the FC was at zero. We were able to lift all the stains but I think the chlorine was too low for too long? Thank you for any guidance you can give me.

 

[needsajet]

Welcome to TFP! Well done first post. It's obvious that you've done your research!

Raise your FC to 5 ppm to be on the safe side while figuring out the CYA.

Visible algae tells you that you're going to need to SLAM per this method: Pool School - SLAM - Shock Level And Maintain
(don't let that picture in the article throw you off; we do this to our pools only when needed, but our pool might appear to be really good when its done.

Do an Overnight Chlorine Loss Test (OCLT) per this method: Pool School - Perform the Overnight FC Loss Test (OCLT)
This will confirm the presence of algae using up chlorine

For the CYA test, try these tips:
- hold viewing tube by the top with thumb and forefinger. You need lots of light to get in to illuminate the suspended whiteness.
- back to sun, tube at waist height in the shade of your body
- measure the same sample several times by pouring back into the mixing vial, then a shake, then re-test.

Come on back with any questions that come up. Good to have you here

 

[doc8404]

Several of us have posted the control reads at 40.
I can clearly see the dot at 50.

 

[mgmoore7]

I am finding the same thing and posted here:
Using Standard CYA - Dot disappears at 40, not 50

 

[Traciecmom]

Thank you for your responses. I retested the control CYA outside yesterday with the sun at my back & it read 45ppm. So I then tested my own water & my CYA was around 30ppm. I added some liquid chlorine during the day bringing up my FC to 7ppm so that I could test for a loss at night. I started my OCLT at 9:00pm & @ 9:00am it had dropped from 7ppm to 3.5ppm. So it looks like I need to SLAM my pool. Thanks again

 

[cj3737]

I started my OCLT at 9:00pm & @ 9:00am it had dropped from 7ppm to 3.5ppm. So it looks like I need to SLAM my pool. Thanks again

Unless you are planning on slamming right now, I would do another OCLT but do the 2nd test before the sun comes up.. You may have had just enuf burn off between sunrise and 9am to skew the results and may find its a bit closer than 3.5. You still may have to slam but it might be a short one.