They will need to be fed, and are sloooooooow eaters. You can put a dome over them, feed them and wait an hour until the food is completely out of sight, take the dome off and watch a cleaner shrimp come over, reach into the mouth and yank the food right out.
Been there, seen that. :evil:
Very aggravating, but if you can keep them well fed they'll inflate and look gorgeous.