Back up to 16 or even 18 if you want...
You can test for cya now... just be warned.. the test doesn't calculate anything in between the lines so if the dot disappears between 30 and 40, your cya is 40.
You can practice this a few times just to get the hang of it... take your test then dump it back it back in the tube and try again... practice a lot so you can get good at it...
Back to the sun shading the beaker, held about waist high then look straight down the tube and watch the dot disappear.
It doesn't actually disappear, the cloudiness of the water just makes it look like it disappears
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