Hey Don, I'm having trouble finding more subjects on this topic so I'm hoping you'll see this bump.

I have been planning on doing a 35 gallon hexagon with a "water substrate". Ideally, I would like to keep killifish in the aquatic part of the tank. I was thinking about covering maybe 1/3 to 1/2 of the aquatic part with flat surface.

Bad idea? good idea? flush out the idea more?