I've had my eye on the tip burn for a while now, I'm attributing that to the constant drip without runoff. The lights are off in the cabinet right now so I can't check, but I don't think that the white parts would be dry and crumbly. If you look it's on some of the lower fan leaves as well... I'll check it out when the lights come on. I definitely didn't expect it to get better, and I can't really move them any further away from the lights, so that plant is just going to have to tough it out.