why do oscars sulk. what could be the reason my oscar is sulking he sits at the bottom of the tank and is not active he still eats just not as excited. All the other fish are fine and, params are fine. the only change recently was i took out the canister in the canister filter with the charcoal, because i was treating for ick. but now it is back in. what is his problem. lol just wanted to know what the problem is and how i could fix it.