I have no clue why they do that but sometimes all my bichirs freak out. Yesterday i come in my room and suddenly all bichirs smash around in the tank like crazy, one even went upwards crashing against the tank lid...it looks like no one was injured but i have no clue whats going on...they are normally very calm and then freak out at random times. Worst of them are my laps and the big ornate.