I think I'm having the same problem
When I excavated I had rock on the bottom of the pond
My gut told me to ripe it out and compact it with clay
But time and money was an issue, mostly time.
I'm Also a little more the half full (or half emty )
I'm hopping that the bottom will seal itself but I'm running out of patience.
You must believe one day all your hard work
will pay off
