Since the sand looks great with one, that may mean he's getting his fill. I wouldn't chance another (definitely not two IMO
) since they both might starve. They seem to do fine for a while - even one- until they eat up everything and starve. Might try to stick a meaty treat under him every so often. I've heard you can supplement them that way.
Once you start to see sand stick to his body when he comes up, that seems to indicate his body is starting to waste away for lack of food.
I've lst three over the last year or so. Doing fine for a bit, then die off. I'm sticking to Nassarius Vibex snails now. They do a great job under the sand.