How clean is your sand bed? Old bulbs don't help, but they aren't the food source. Pruning it back is a good defense.If it gets out of hand it gets worse fast. Outgrowing and die off will spur on further growth.

I have seen my emerald crab once. While I was moving the tank and it shocked the heck out of me since he is 2 years old. I never find molted skin either. Who knows what he does for a living.