I have 8 small dempseys (maybe an inch). The tank is filled with rocks and slate making many nice caves. Everytime I walk by the tank the fish dart into a cave. In fact the only time I see them is if I lay on the couch for at least a half hour and dont move. I have adequate filtration, I feed them three times a day and do weekly water changes of 15-25%. The water chemistry tests perfect. The last time I had dempseys they were very aggressive and would even attempt to bite me as I changed the water. Is there something wrong? I have had them for about three weeks, so I would think they would be adjusted.