NO, NOT TABLE SALT!!!!!
There is a large difference between table salt and aquarium salt!!!
No, go ahead and vacuum the gravel. The worst dirt settles under the gravel causing ammonia spikes.
How often is his water changed? It's hard to see the color of his fin edges but as a crowntail they look a little feathered. He needs to be in pristine water, warm and changed 50% once a week (for a 5g).