In the past two days, a whitish band has developed along the waterline of our pool. Can anyone shed light on what has caused it, and how to possibly get rid of it? The wall surface is painted concrete, so I'm concerned about serious scrubbing). See the picture below, and below that, numbers from yesterday's water test (TF100 kit).
Numbers from yesterday's water test (I had a 1 ppm FC loss overnight prior to the test):
T/A: 150 (down from 170 from last week's test)
CYA: 40 (note: CYA should now be at @50, as I added 14 oz. stablizer after the test)