ive been noticing at night one of my angelfish have been making some noise, he will pop his mouth out of the water and suck up some air and shoot it out his gills. is this normal? should i be concerned? or is he just playing?. its mainly at night, sometimes during the day. im assuming hes playing, or likes the feeling, but i just want to make sure its not a sign of something i should correct, or give him in anyway.