What is this Black Spot


Gold Supporter
TFP Guide
Jul 21, 2013
Northern NJ
Welcome to TFP.

We need the rest of the story. Is that black spot the only one in the pool? What is the history of the pool? Where is it located in the pool? Can we get a wider pic showing where the spot is? What size is the spot?

What is your water chemistry? What test kit do you use? How do you chlorinate your pool? What chemicals do you use in your pool?

A lot can be answered by creating your signature with details of your pool and equipment.

You can read...



TFP Expert
Mar 2, 2011
Possibly iron bleed though from rebar or a wire tie. Try a strong magnet on the dark brown spot to see if it sticks.


New member
Jul 15, 2017
Thank you for the reply! I will create a signature, read the article you suggested, and create more detailed posts. I appreciate all the information on this site.


TFP Expert
Mar 2, 2011
The only thing you can really do is to cut out the area and the metal and fill it back in with new plaster. It might eventually bleed through again if the metal is near the surface.