CYA Tube Pic...Black Dot

[wkusae31]

I am a newbie to testing. I have tested 5 times now within 2 weeks. Can you help me determine when the "black dot" is gone for the CYA test? The tube on the left is 50 CYA. The tube on the right is 45 CYA. 50 CYA tube has a faint trace of black dot. Am I being too anal about this? Which CYA level do the experienced folks think I have in that tube?

 

[jblizzle]

It should be completely gone. I still see it a 50 ... maybe even 45.

 

[Patrick_B]

It's a little subjective, but there no difference in 45-50. If you think it leans to 50, choose 50, or vice versa. The margin of error is 10-15 PPM. You're being anal. :lol:

Good to be accurate, but this test is not laser precise.

 

[wkusae31]

It's a little subjective, but there no difference in 45-50. If you think it leans to 50, choose 50, or vice versa. The margin of error is 10-15 PPM. You're being anal. :lol:

Good to be accurate, but this test is not laser precise.

Lol. I majored in Chemistry and Math in college. Precision has been hammered into my head, and I've become more "by the book" as I age. Haha.

 

[JoyfulNoise]

I say 45 looks more faint than 50 (I can still see the dot at 50ppm). So I'd ere on the side of caution and call your CYA 50ppm. Since you have an SWCG I assume you're trying to get to 70ppm, correct? Or are you trying to SLAM? Depending on what you're trying to do, I might call it 40ppm since that would force you to add more drops to make it completely gone....

One thing that might help is to buy the 50ppm CYA standard solution (I think it's either on Amazon or TFTestKits or both?) and play with that to "calibrate" your eyeball. I mixed up my own standard (70ppm CYA in distilled water) once and found it useful in helping me to gauge the dot....

But @Patrick_B got it right - the margins on this test are wide so 40 or 50 is not going to kill you.

 

[wkusae31]

I'm just trying to raise CYA and not doing a SLAM.