Okay, so I have a 40-gallon tank with 1 blue gourami, 6 gold barbs, a Senegal bichir, rts, a pleco, and a stripped raephel catfish. The catfish, barbs, and gourami are all about 2-2 1/2 years old. Last night I fed them and everyone was hungry and voraciously snapping up the food. This morning I turn on the lights and everything seems fine (It's possible I didn't notice a dead fish), I go upstairs to have breakfast, only to come back down 3 hours later to find one of my gold barbs dead, pale, and floating face-down in the plants. (This was one of the biggest of the six.) A few days before I did a 25% water change, and have been keeping the water quality up constantly. I also have a second filter on this tank. Does anyone have any clue as to what might have happened? I was thinking old age since gold barbs average out at 3 years, so it didn't seem too crazy for it to die at 2 1/2.