I'd also worry about splashing water while cleaning it.
As for heat rising through the aquarium floor, I think they could've minimized that by adding some active cooling between the acrylic ceiling of the PC section and the glass floor of the aquarium. Even so, you still would want to put fish in it that are good with water temps above room temperature.
An interesting concept might be if there were some tropical fish that actually needed warm water, and you ran the PC's water cooling lines through the aquarium section (in heat-exchanger fashion, so there'd be no mixing of the cooling vs. aquarium water). The PC would effectively be a water-heater, although you'd need a thermal probe + some software to throttle the CPU/GPU clocks if the aquarium water got too hot. You'd also need a background mining job (or a backup heater) to kick in, when the water gets too cold. Better yet, this could also serve as a solution to the splash hazard posed by all of the holes in the base - just don't have any holes!