I have six marble hatchets, they're at the top 95% of the time, the other 5%, they're swimming at the mid-level or playing in the bubble wall. When they're not swimming, they're normally at the top though, they face toward the current from the hob filters and the bubble wall, so they pretty much stay in place. I don't think they're that active while at the top. I've been waiting to see them jump, none of them has. I figured they'd jump by now since everyone says they're very likely to.