Pond seepage problem

I built a pond (fountain) that has a concrete base with concrete blocks
around the edge to create the pond. Despite that I treated the block
with some water sealer I get seepage to the exterior of the blocks. Is
there any type of water treatment that I can add to the water that will
stop the leagage. The inside of the fountain is tiled so the treatment
must enter via that grouted area.

Thanks,
Wayne Gregori