when my bgk was smaller I used a 12" hurricane lamp glass tube. You should be able to get one from a large lighting centre I siliconed some fake plants onto it aswell
The clear pipes and hurricane lamp covers are pretty much a no no, it doesnt give them any protection for the light, If you want to see them lay a flat light colored rock against the glass, I need to get a light colored rock.
I got mine from one of those rock fountains you can buy at walmart, but thats another story, try looking at a tile or flooring company, Thats about all I can think of.