Circular spot at the bottom of fiberglass pool

[Jay_8848]

2-3 inches in diameter white circular spot at the bottom of the pool. When I felt it it was smooth and this spot/stain is just in that place, there are no other stains in the pool.
Does anyone have any idea why there is that spot? Is this normal in a fiberglass pool? Recently moved so do not know the history of the pool.
Thank you in advance!

 

[ajw22]

Looks like someone let a trichlor tablet sit in that spot too long.

 

[Jay_8848]

Looks like someone let a trichlor tablet sit in that spot too long.

Thank you, do you know if it will remain just as a stain or degrade further? Do I need to take any action? It's okay for me if it's just a stain.

 

[ajw22]

It will probably stay as a birthmark.

 

[JamesW]

Maybe a stain and maybe a delamination bubble.

Can you tell if it is raised even a tiny bit?

 

[Jay_8848]

Maybe a stain and maybe a delamination bubble.

Can you tell if it is raised even a tiny bit?

Not raised even a tiny bit, compared to the neighboring bottom surface I don't even feel a transition, very smooth.