Can I keep this n pour sound in the empty area
How do I avoid gas
Can that kill my fish
The gas comes from junk sitting in pockets with no oxygen in them. If you vac or stir the sand or have fish/snails that do it for you or pump fresh water under the sand you will avoid the problem. I do not know if geos dig all the way to the bottom of the tank, I have never kept them.I have a reverse undergravel filter and burrowing snails, so I don't have to worry about it, but I'm assuming you don't, so don't encourage hills unless you want to gravel vac frequently. Gravel vacing will slowly kill your plants.