Very cool.
An interesting trick I learned (i have only done with very large glass bottles but assume same laws apply) - put a knife blunt side down in the bottle and fill about 1/4 - 1/3 of the way with water. Lift it up and slam it down, on the air…not a hard surface that would just break all the glass, there should have been enough force to completely knock out the bottom of the glass. If it is like welded or whatever, it will be a clean break. Provided you can do this without having any issues, should make for a pretty cool tunnel for your fish!
Anybody have any tips for getting a little piece of glass off of the side of the bottle? I really liked the pic with the encrusting acro coming out of the side of the bottle and would like to try something similar.