I used glazed ceramic tile in several of my ray tanks without any issues (look up some of my old threads with pics). Just cut them to fit the bottom - no glue no grout. Didin't have any issues with water quality or waste getting underneath the tile. Make sure you used smooth glazed tile and not rough or porous tile. Algae grows into the porous and rough tile making it hard to keep clean. When I moved I painted the bottom of the tanks before setting them back up so I don't use the tile anymore.
Thanks a ton. Very helpful