Check your nitrates/phosphates. Snails hate both. If not then he could've been dud, and will simply now become a new home for one of your hermits. Yea, I'd pull it out completely. The problem is that the coarse sand will always make it's way to the top, and become a sediment trap. As far as for what to replace it with, that's entirely up to you, but if you do go with sand definitely the smaller the better.
DJ