This betta is starting to worry me. He used to hang out around the top of his bowl, usually perched on top of the rock in his bowl. I change his water every week or so, and after the last change he's been acting really skittish. He never comes out from under his rock. When I am able to coax him out with food, he'll come up to the top to grab it and then he'll dart back under his rock. He doesn't appear to be sick at all. Every once in a while he'll come out, dart around the bowl really fast and then go back to hiding under his rock. My first thought was that he may have a bubble nest inside the rock and he's staying under there to protect it. But he hasn't acted that way with any previous nests and I can't see under the rock to confirm that. I need to change his water again but I don't want to make him even more neurotic than he already is by moving him around. Any thoughts? Sick? Scared? Psychotic?