I would say acclimation issues are the cause. I usually initially turn the powerheads off and gradually ramp them up over a week or two. For lighting, the most important part IMO, I put a few layers of paper towels on my top and take one layer off every few days. If you did something similar, who knows? Most of the time it ends up this way and all you can do is hope for the best.
Whatever you do, dont force it. Give it another week, try feeding SMALL bits. All else fails, point a small powerhead at him to coerce out of the cave.