Right product to use to seal a leaky concrete water feature?

I have a waterfall feature on a backyard swimming pool. The feature is made of concrete (textured to look like natural rock) and sports two approximately bathtub sized basins. The lower basin has developed a pretty hefty leak that I am unable to pinpoint. I know it is on the bottom somewhere because all of the water leaks out in approximately 5 hours if I let it sit.

I have tried a couple of different paint on applications, one that was latex based and billed itself to be for “wet wall” applications and would stand up to hydrostatic pressure. The other was “plastidip”, which is a spray on rubber like coating. Neither has done the trick.

So… any of you jellies out there know of a product that would do the trick?