For the last week my dwarf gourami has been acting weird. When the lights are on he is almost completely still and just sits at the bottom of the tank. When I shut the lights off at night it's almost like he comes back to life and starts roaming around and plays with his toys.
What in the world could this be? I have had him for around 4 or 5 years now and he is as big as my hand.
He has his own 55 gallon tank with just a bottom fish. I had to put a partition in about a year ago because he kept stalking him. No other fish in the tank.
nitrate, nitrite, hardness, PH and alkalinity levels check out fine. The water is a tad hard but nothing he isn't used to. Not sure why turning the lights off make such a big difference. Any help would be appreciated.