[cheseboy]

I think the best idea is to drill a hole through and attach a suction cup to the hole. Then cover the cup with the substarate to make in not visible. Also what is wrong with just having a plain airstone distribute the co2. Also I don't understand why you would need an airstone for the air underneath the shell. Why not just have a tube since it dosen't matter what size bubles go into the shell theyr all going to form 1 big bubble when they get there.