I'm planning my 20g puffer tank which will have 6 bumblebee gobies but want adequate homes for them. Has anyone ever tried walnut shells boiled and hollowed with entrance hole?? Any reason why this may be a bad idea?
I think you're being optimistic in thinking that they'd hang out in the shells. They may be tiny fish, but they (mine, at least) don't confine themselves to small spaces. They explore the whole tank, venturing in and out of caves (terracotta pots), sitting on the leaves of the plants, on the glass of the aquarium, etc. I have no idea if the shells would be harmful, but I'm just not sure how useful they'd be.