Help me ID this stain.

[djdonte]

I usually get stains like this from berries, but the chlorine makes them go away over time. These have been there for a few months now. Rubbing a trichlor puck on them does nothing, nor does vitamin C. I was able to get them to fade quite a bit with a red "erase it" bar, but I didnt want to go too crazy since its pretty much a pumice stone. I also have a gum eraser that did nothing. These are relatively new stains, so I know it's not rebar from below, but they do look like rust. There are maybe 5-6 spots like this but these are the best pictures. The finish is Quartzscape Super Blue maybe 3-4 years old.

 

[Texas Splash]

Maybe something copper related fell to the floor? Do you have any dry acid (pH Down) around by chance to test? Going back to iron and the Vitamin C test, to rule out it's nothing metal bleeding "up" from underneath (i.e. rebar), see if a strong magnet tried to stick to that area.

 

[djdonte]

I dont have dry acid. I'll try the magnet, but I'm confident its not rebar, or else it would have shown years ago, not after more plaster was added on top.

 

[Texas Splash]

Did chlorine or Vitamin C testing actually make the stain worse or darker? Sometimes that can happen with copper as well.

 

[djdonte]

Chlorine had no effect. The sock with vitamin C was about a week old and just kept causing red clouds. That didn't happen when the pills were new. Maybe I should try new vitamin C? Where would copper come from? I have no history of copper in my city water and I dont use algaecide.

 

[Texas Splash]

Where would copper come from?

Perhaps unlikely, but I'm just looking for clues at this point since the chlorine tabs and Vitamin C didn't seem to help. You could try a new batch of Vitamin C just to be safe. But you might end-up needing to try one of those Jack's Magic ID stain kits.

But those marks look like something hit the surface when it sank and bled outwards. No recent metal work or landscaping perhaps where something could've gotten blow into the pool?

 

[djdonte]

I had my roof replaced last November but they covered the pool and I checked after as well for nails. Other than lawn mowing and shrub trimming no significant landscaping. I think I will try some new vitamin C since it cheap before I buy the Jacks kit. It does look like rust from a nail or something sitting there but I really don't think that's the case. Even if it was, my robot works pretty good and I would have found the nail in the leaf catcher or pump strainer.