My Reed fish found out how to get down there, as well. When he's hungry, he comes out. If you really don't like him down there, you might want to try making a very secure place for him to hide above the substrate. When he comes out, block him from going back. He just wants a dark, secure place to hide. My Reedfish has been doing this for months. I finally decided to jut let him be. If I put frozen bloodworms, brine shrimp, human food type shrimp, or ground up beef heart in the tank, he comes out very quikly. I hope this helps.