I went on a 5-day trip to Death Valley (just came back). Figured that the fish could live for 3 days without eating anything, and I didn't want to risk polluting the water with vacation feeders. When I came back yesterday, it turned out that heater either malfunctioned, or since the thermostat was off in the house, the room temperature must have affected the tank...anyways, the temperature was 72 degrees Fahrenheit and the fish were half-dead. The danios were all pale and lying on the bottom, the kuhli loaches looked like if they were dusted with charcoal, both serpae and Pristella tetra were whited out and hiding in the cave...the only fish that seemed unaffected were the peppered cory and the glass catfish. The cory should have been fine because it could handle a wide range of temps, but why the glass catfish were fine (being the most delicate fish, but had no opaque spots, even had a iridiscent sheen) was a mystery to me. Once I turned on the tank light and cranked up the heater a bit, the fish started to instantly recover (another mystery). In a matter of minutes, the danios were actively swimming again (not fully colored up though) and the kuhli loaches were to. Just to secure this, I added half a dosage of Amquel + as a stress coat. By today, all of the fish were perfectly fine. Does anyone know why my danios nearly expired (though they are coldwater fish), why the glass catfish were fine, and why they started recovering almost instantly when I came back? Sorry for the long post, but I am completely baffled.