Tested again today in this way. when it gets to 60, black dot disappears for about 2 seconds then vaguely visible again. At 55, it's not visible even after 10 seconds. So is this 60 or 55?Cya has to be tested with your back to the bright sun and the sample waist high in the shade of your body.
Since CYA seems no longer problem, plan to vacuum thorough and refill again tomorrow to reduce CYA a bit and then add more borax to get PH to right range and then SLAM on Sunday.