Stubborn stain

Jaxbchjim

Member
Jul 8, 2015
8
Jacksonville, FL
A dark stain appeared on my Pebble Tec marcite back in early spring, about 18” long and 12” wide in a fan shape. From above the waterline it appears almost black, but underwater it looks grey/brown (see underwater pics attached).

I first tried rubbing a chlorine tab on it with no results. Later applied muriatic acid via a PVC pipe. The acid temporarily lifted it but it quickly re-deposited in a larger area as the acid drifted toward the deep end. Now it’s about 4’ long. Strangely subsequent treatment with muriatic acid did not affect it. It’s like it has a stronger bond now.

Thinking that it may be iron, I later tried ascorbic acid. Brought pH down to 7.2 and chlorine near zero, put about a half pound in a sock and rubbed it directly on one section of the stain for several minutes, until the AA completely dissolved. No effect. Poured the remaining 1.5 pounds of ascorbic acid in the water over the stain and let it recirculate for a day. Still nothing.

I should add that there are other areas of the pool that appear to have lighter staining than this area, as if there is lighter accumulation of whatever this is. I am not on well water. The pool was constructed 5 years ago.
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thanks in advance for any guidance.
 

JamesW

TFP Expert
Mar 2, 2011
21,145
I suspect that it's probably copper.

Do you have any sources of copper?

Copper is difficult to remove.

Maybe get Jack's Stain ID Kit to confirm.
 

Jaxbchjim

Member
Jul 8, 2015
8
Jacksonville, FL
I suspect that it's probably copper.

Do you have any sources of copper?

Copper is difficult to remove.

Maybe get Jack's Stain ID Kit to confirm.
I don’t have a heater and have never used algeacide in this pool, so not sure where copper would come from. My only guess would be maybe the product used to stain the Rico Rock coping and waterfall, which is sorta copper-ish in tone (you can see it in the pic where my dog is in the pool). Seems like a long shot, but maybe?

I used a Suncoast stain ID kit a while back with no luck.
 

JamesW

TFP Expert
Mar 2, 2011
21,145
The original plaster had green specks. So, that makes it difficult to detect copper. The plaster looks like it has a lot more green.

You can try some Jack's #2 copper and scale stuff (sulfamic acid) on the spot to see if it works.