Help Identifying Stains - Rounds Grey/Black Dots on plaster

[Valhop14]

I need some help in identifying some stains in my pool. It is a salt water pool with plaster/quartz surface.
We had the pool resurfaced last season but all of a sudden we are seeing a number of round spots which are dark grey in color. I think they might be some kind of metal stain but how do i determine what exactly?
Any help would be greatly appreciated!!!

 

[AquaDoctorLLC]

Re: Help Identifying Stains - Rounds Grey/Black Dots on plas

Pictures please.

Could be black algae. Does it feel slimy? Can you "scratch" the surface and it feel less slimy?

 

[Valhop14]

Re: Help Identifying Stains - Rounds Grey/Black Dots on plas

I'm almost sure it's not algae, it doesn't feel slimy and it doesn't budge when brushed.

 

[susa]

Re: Help Identifying Stains - Rounds Grey/Black Dots on plas

>> seeing a number of round spots which are dark grey in color

what size, pencil eraser, thumb, palm size ?

 

[Valhop14]

Re: Help Identifying Stains - Rounds Grey/Black Dots on plas

Size: ranges from dime to quarter size