whitish band at waterline


LifeTime Supporter
Jun 3, 2010
Dear All,

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).

all best,

Numbers from yesterday's water test (I had a 1 ppm FC loss overnight prior to the test):

FC: 4
CC: .5
TC: 4.5
pH: 7.3
T/A: 150 (down from 170 from last week's test)
CH: 210
CYA: 40 (note: CYA should now be at @50, as I added 14 oz. stablizer after the test)


Mod Squad
TFP Expert
Platinum Supporter
LifeTime Supporter
In The Industry
Apr 1, 2007
Sebring, Florida
Well, it's pretty much guesswork, but I would say you have some Calcium coming out of solution.

Your CH is not too high and there is nothing in your numbers that would indicate a problem.

It looks like it will take some brushing, scrubbing to remove. (I hear you about the painted surface) I do it sooner rather than later.

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