Black smudge on pool walls


Well-known member
Sep 8, 2015
Dallas Texas
I have a black “smudge” on the wall of my pool in a couple of spots. It reminds me of rubber/brake residue. It comes off when I wipe it with my hand but brushing doesn’t seem to get it off. Any thoughts? Is it just dirt (lots of construction around here ) or something else?

My pool details
Chlorine is 7 (usually have to add 1-2 ppm every 24 hours but that hasn’t changed)
CYA 40.

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
Jun 22, 2014
Texas, San Antonio/Marion, South-Central Area
Pool Size
Salt Water Generator
SWG Type
CircuPool RJ-45 Plus
Sounds like a scum line we can get at times. No real rhyme or reason. We can try to blame excessive oils in the water during swimming season, but sometimes it just happens. I usually get it once or twice a year on one corner and perhaps in the skimmer. We use a little elbow grease and perhaps a Magic Eraser to remove it on ours.
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