I'm still personally going with the water change but I could be wrong. I use a 5g bucket to remove and add water back to the tank with prime to dechlorinate. There was an air stone in the tank at all times, previous pics can show that I just took this pic once everything was unplugged. The levels in the tank were terrible when I got home but there were 6 decent sized dead fish in the tank for who knows how long cause this little tank made my whole house smell. It was like death when I walked in the front door. With the heater it could have been but I personally dont think so unless it was an electric short that just got them all quick. The temp in the tank when I left for work and when I got home was its 72 I set it at. I was only gone for about 7 hours between the water change and death throughout the tank. I can try and justify it or whatever but at this moment I dont really even own any fish anymore and don't plan to for a few years so I am just going to lay this one to rest and call it a $1500+ loss...