I've had a pair of blue gouramis in a 75 gallon tank for about 5 weeks now. Up until yesterday they were peaceful enough but yesterday the smaller of the two started attacking the larger one. The large one doesn't have much left in him. He's kind of floating near the top of the tank or resting on the sand. Once I even found him stuck to the filter intake. I imagine my next coarse of action is to isolate one of them. I'll pick something up tomorrow since I have nothing to use at the moment. Hopefully the poor guy will make it another day. Should I be isolating the aggressor or the victim in this case? What would cause the smaller one to suddenly behave this way? I added 2 Dwarf gouramis to the tank just over a week ago. The smaller blue is picking on them a little but not enough to cause any harm. Is there any way to correct this behavior or does one have to go back to the store?