[katieHaylor (OP)]

John says:

I am building a large pond and plan to spread a limestone gravel around the shoreline. The pond will be filled with rainwater and I was wondering how long it would take for the rainwater to start to dissolve the limestone and impact the pond water pH? I am hoping over time for the pond to have alkaline water but not sure how realistic this is.

What do you think?

[Bored chemist]

It's hard to say but my guess is it would be reasonably quick- a week or so.
You could speed things up by adding crushed lime.
How big is the pond?

[axscientist]

You can add an acid to speed up the dissolving process, since by adding acid, the limestone will become soluble in water and thus be able to dissolve. Carbon dioxide can dissolve into water to form carbonic acid, which also works.

[Bored chemist]

I am hoping over time for the pond to have alkaline water

You can add an acid

I don't think you understood the problem.