As for mine, they dig a pit in my Eco Complete substrate and lay their eggs there. Wish they would spawn on a flat surface I provided, but they don't. At least mine isn't, lol.
But my female has an injury now, and don't think she's going to make it. Just remember one thing with your GBR's, if any of them get an injury, like a small chunk taken out of them by another fish, it's all downhill from there. Even if you QT and medicate them, they just seem to lose all their will to live. I lost 1 male due to my red tail shark, and now a female, the only female. So I've ordered a bunch more GBR's, 7 females and 3 males, as I'm hooked on breeding them, as well as Bolivians. And I've got some fry from both in my fry tank now.