Need suggestions on fixing small hole in bottom of plaster pool

[Ahchoo]

Have a salt water plaster pool that appears to have a quarter size hole in it (at the bottom) with what looks like a liner behind it. Looking for thoughts and recommendations on fixing the hole such as products/brand to fix and any steps to take. Pool is not empty, has water in it.

 

[gwegan]

Could we get a picture? Have you probed the indentation? What does it feel like? How old is your pool? What does the rest of the plaster look like?

In a plaster pool there should be concrete behind the plaster not some type of liner. So while I have some speculative ideas without a picture and more information I'd be shooting in the dark.