I have 6 Tiger Barbs in a 30 gallon tank, 3 green, 3 regular. The tank is cycled, water parameters are 0 ammonia, 0 nitrite, 40-60 nitrates. All the other barbs besides my biggest one are swimming around normally and nipping at each other every now and again. My biggest one is constantly hiding, darting around the tank, and has been acting like this since I introduced them into the tank. He never comes out to eat either. It's been a week since he's last eaten. What should I do?