Hello I have a 45 gallon established tank that has one baby rts, one siamese flying fox, one small koi angelfish, 3 black tetras, and 2 white tetras...lately I have noticed that my tetras have been congregating in one corner of the tank. This is weird as they normally are swimming all over the place. They look healthy and I feed them brine shrimp and new life spectrum pellets alternating everyday...just tested my parameters and they are as follows 78.5 degrees, 0 ammo, 0 nitrite, and less than 5 nitrate. Anyone know what's going on?