You're right JackFrost, under normal circumstances the fish probably would have been fine, but the aquarium is fully covered with the light and the filter component, and therefore even just oxygen from the room couldn't penetrate the surface water. The water condition was ideal, and the fishies were fed properly. Afterall, they're goldfish. They should be pretty hard to kill. I felt horrible seeing 4 of them floating at the top. I still haven't figured out why both the filter and the oxygenator crapped out. They're separate units running independently of one another. Who knows, maybe it's the impending full moon. Thanks for your input.