Red/copper Stain

duraleigh

Admin
Mod Squad
TFP Expert
Platinum Supporter
LifeTime Supporter
In The Industry
Apr 1, 2007
34,477
Sebring, Florida
I agree with JamesW. It looks like iron and viamin C (crush up several and put them in a sock and then directly onto the stain) will remove or minimize it.
 

setsailsoon

Gold Supporter
LifeTime Supporter
TFP Guide
Oct 25, 2015
3,661
Stuart/FL
Pool Size
12800
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
CircuPool RJ-30 Plus
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JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
17,446
Tucson, AZ
Pool Size
16000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
Try using some dry acid in a sock to rub the stain with. Be careful though as you don’t want to over etch the plaster.
 

JamesW

TFP Expert
Mar 2, 2011
21,568
It might be iron embedded in the plaster and bleeding through.

Try putting a strong magnet on the bigger spot to see if there is any attraction.