Remove the gravel, I seen so many salamanders in captivity that die or go through a lot of pain passing them from swallowing gravels and small rocks.
Peat moss or coco fibre is best for them. I give them about 4"-6" of water, float food container with coco fibre mixed with moss. I used to keep them in a tub of about 50lbs of coco fibre, but I gave away all except one.