I come to think of "the Screaming Skull" from 1958.
It doesn't fit the bill on all points but it features an outside garden(looks like, AND sounds like a jungle) pool, which bubbles and is covered in an eerie mist most of the time. The pool is featured quite a bit in the film as it can be hypothesized to be the dwelling of THE screaming skull, a man dies there and the lead lady sits by it at least once. The said man is trying to drive the woman insane by way of the skull...
As I said earlier it doesn't sound exactly like your description but the pool/jungle/woman/death thing is there. If not at least it's an entertaining movie, with it's "We'll pay your funeral, if you die of fright!" -insurance before the opening credits!
The second movie is the classical "The House on Haunted Hill" with Mr Price. I guess you have already ruled this out... Nonetheless it contains an acid pit (though indoors) in which a money hungry woman ends her days - right towards the end of the film.
I would go for the Screaming Skull though... It was featured on the Mystery Science Theatre 3000 I have heard...if that helps.
Hope you find, whichever movie it turns out to be!