My betta fish, Avi, hasn't been acting like himself lately. He used to swim all around his tank, but now he usually just sits at the bottom of the tank, sort of burrowed into the plants. He still loves to eat and for food he will swim up to the top, but then he'll slowly drift to the bottom again.
He does look as though he's lost a little coloring, especially in his face and near his gills.
Does anyone know what's wrong with him?