This is the info from 511 Porous Plus--a penetrating sealer designed for the protection of the most porous surfaces. 511 Porous Plus forms and invisible barrier that is resistant to moisture and stains while allowing vapor to escape. 511 Porous Plus is not a surface coating and will not alter the natural look. All surfaces are harder and less slippery.

It lists concrete as something it can be used on.

This sounds like it would seal the waterfall but it says nothing about how it would effect the fish/life forms in your pond. Is the pond under construction or completed?

I could find no info on the other sealant and concrete.