Staining caused by chlorine shock.


Well-known member
Dec 23, 2012
Manassas Park, VA
In July of 2012, I applied Power Plus Powder shock directly to my pool (Gunite pool). However shortly after it was applied we lost power for approximately 12 hours. When I checked on the pool the next day there were dark stains on the bottom where the shock laid on the bottom. I have still not been able to remove the stains.

For approimately 2 months before this I was using a weekly dose of Copper Algaecide for maintenance as well (left over from the opening kit).

From research it sounds like this could be metal that has attached to the pool itself, however a couple treatments of Metal Out did not seem to have any effect on the stains.

Is it possible that this could be some kind of stain cause by the shock sitting on the pool bottom for such a long time?

I plan on using a regular treatment of the stain remove in the link below to see if this provides any results. ... 14222.html


TFP Expert
LifeTime Supporter
Apr 4, 2009
Welcome to TFP. I do not see copper listed as one of the metals, the attached product can treat. Also, I would never advise you to add anything to your pool water that you do know the chemical components. 1st try holding a vitamin c tab against the stain to see if it lifts...if so it's likely metal staining.

also never use copper based algaecide, eventually it will turn blonde hair green :<(



TFP Expert
Platinum Supporter
LifeTime Supporter
May 7, 2007
Silver Spring, MD
Chlorine sitting in direct contact with the surface of the pool can cause stains or damage in various ways, including causing metals to deposit in the immediate area. It does sound like you might have copper staining, though it is difficult to completely rule out several of the other possibilities. Dark copper stains are especially difficult to remove. The most effective approach is to drain the pool and acid wash the surface, which however shortens the life of the plaster and can be expensive.


Well-known member
Dec 23, 2012
Manassas Park, VA
Thank you everyone for the reply. Based on similar threads I believe I have a list of actions I can take once i open the pool.

The first is to balanace the water correctly, and keep the ph a little on the low side around 7.2.
Add Metal Free to the weekly maintenance.
Then I will try to confirm that the stain is a copper stain. Not sure how to do this however I can test if it is an iron stain by using a vitamin C tablet on the stain.
I will then try some spot testing with muriatic acid (either by placing it in a sock and letting it sit on the stain for a minute or two, or by using a sprayer).
If all else fails I will be looking to drain the pool (after confirming the hydrostatic valve is in working order), acid washing, and paint the pool.

If it gets to this point I am leaning towards using the Dura Seal, One-Coat Epoxy White paint from Leslie's.


Mod Squad
TFP Expert
LifeTime Supporter
May 19, 2010
Tucson, AZ
FYI, General consensus seems to be that painting a pool is a temporary fix ... likely only lasting 2-3 years before it starts to peal. Plus any irregularities in the pools surface will still be visible ... paint does not "fix" surface irregularity, just changes its color.


TFP Expert
LifeTime Supporter
In The Industry
Jul 25, 2011
The stain is probaby copper, which turned black (copper oxide) on the surface after you added the chlorine shock.
I suggest purchasing some "potassium alum" granular (two or three pounds) and sprinkle it over the staining. It should remove the black stains very quickly. Vacuum to waste any residue on bottom after that, or clean filter a day later.
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