CYA doesn't make sense

[KKell]

Hi,
i started my pool about a week and a half ago and added enough CYA to get the levels up to 35. My kit came in last Thursday and I measured a CYA of about 30 (dot disappeared with full tube). We had some rain and I backwashed my filter once, taking maybe 2 inches out of the 45 inch water level. Because I was losing a lot of chlorine in the sun I decided to raise CYA to 40 and last night I put in another 48 oz of liquid CYA. I just measured it now and even with the tube all the way full I could still see the dot. The only possible explanation may be that my water is cooler than 70 degrees I think. I just now read that you ought to raise it to room temperature for testing (by the way, in upstate NY 70 degrees IS room temperature).

is that it or can there be another explanation?

other tests:

FC: 4
PH: 7.7 (will lower that once people are out of the pool)

TA was fine a week ago, assuming nothing changed.

 

[zea3]

Did you try to perform the test again to make sure you didn't leave any steps out? Are you reading the tests under the same lighting conditions? Also you can pull your sample and let it warm up a bit if the temp is below 70 and try again. One more thing, make sure the pump has been circulating the water at least 30 minutes before pulling a sample.

 

[KKell]

I re-did the rest this morning:
i let the pump run for half an hour.
filled up the bottle at arms-length down the pool.
Dumped it out to leave water at the 7ml line and filled it up with R-0013 to the 14 ml line
let it stand in the sun and warmed it up in my hands for about 3-4 minutes.
It is currently sunny and I held the receptacle at hip-height in the shade while looking down.
Filled it up all the way and when the surface is still I can still very faintly see the black dot (not as much as yesterday though.

CYA should be at 45 according to math - it reads less than 30

 

[Patrick_B]

I can't explain it, but if you are confident in the reading, You'll have to add more of you want the increase. I would suggest using powder instead of liquid.

 

[pabeader]

I didn't notice you mention the shaking time....

 

[gilbee]

I recommend picking up a bottle of the 50ppm standard solution if you're unsure about your reading...then you can pour till you get to 50 and see what it looks like, or test blindly and see if you get 50 with your methods. I found that I was getting lower numbers than reality because I was measuring at chest height instead of waist height thinking it didn't make a difference...apparently it does.