Are these sitting on gravel or glass base? I ask because the slate bases seem quite large and I wonder if you will get dead areas underneath, or if you will regularly lift them to siphon underneath?
I too like using slate but have always stacked them, not siliconed them together. Also not used a base, just sit them on the gravel. Siliconing is safer of course as you don't have to worry about a fish bumping the sides and having it collapse on them :-?