Changing Tanks

Hello, I recently got a 6.8G shallow tank to move my long- tailed Betta into. I put him into a 10G for a few months but he doesn’t seem to do well because it is so tall and also noticed a small leak.

Currently the 10G has a bottom layer of stratum, gravel rocks, a piece of wood, and some live plants.

New tank plan is to have stratum at the bottom with sand cap.

Any advice on if I should keep the stratum for the new tank? Or advice how to set up the new without crashing the cycle? I’ve never moved tanks before. Thanks!