Ok so i bought 2 Iridescent sharks 2 days ago and one of them is acting strange it keeps swimming like 100mph crashing into the tank it hides by a corner and jumps from the tank but hits the lid and he/she has been doing this since i bought it. Is it because it's not use to the surroundings, does he/she have a problem or what? (Btw how do i know if it's a male or female) 