Groooovy fellow babies. I had no idea! Great photos. Mine is touching the front glass, so not really a place I'm crazy about the thing taking hold. Interesting to see that others have had similar experiences though. The famous PaulB on RC has a few posts about a glass bottle in his tank that has become encrusted. He scored or sanded the glass to rough it up & make it easier for critters to take hold & encrust. Not something you want to do to one of your tank sides though. I also have a mini glass bottle on the bottom, it's encrusted with coralline, but I didn't score the glass like PaulB did. Took years though.

Kewl, that's kind of where I'm at right now. Will be interesting how things develop! That's an amazing photo.

Thx Mike, just let it be in an area you don't need to touch,,, mine was a complete accident, unplanned.