Funny, mine started on rocks, lime green, then speckles of purple and now specs of purple on my glass bottom. All plastic is completely free of coralline for now, though there's a crusty spray of green coralline on the tank walls. This QT tank is a 13.5 Evo, tooIt won't be on the glass first. It covers plastic parts like powerheads first then rocks. Then glass.
I added a piece of rock from an established tank, which brought me all kinds of goodies, including coralline. I'm only 2.5 months in!