Your place will become impassable if you add any more tanks. Where will the humans live?
This should be a good shape--lots of room for fish.
I will see how the shells substrate looks and behaves in the tank. I filled the tank with 1/2 RO + 1/2 tap. Our tap water is quite hard and I know that this blend still has pretty high GH. I imagine that dissolution won't be so fast and I might even change this tank to 100% tap later on. The material will be sitting right on top of the main gravel substrate, so I can also remove it later on if I don't like it.