Ive have had my 20 gallon set up for a good 6 months now. Only recently i have noticed 1 of my 4 corydoras acting werid. His very skittish and freaks out easily, he breathes REALLY fast if there are ANY types of loudness/sudden movement around the tank. Its like he has anxiety/panic attacks. All my other fish are fine though. I have 4 corys, 1 betta, 6 neons and 2 bn plecos. My other cories like to hide during the day and are active at night. Whats wrong with him? Is this normal?