[Matthias] swapped out his twin-tube florescent aquarium lights for LEDs. By running tank water through the aluminum LED mounts he’s transferring excess heat into the water in the tank, in turn saving some of the electricity that would have been used to heat the tank. Couple this with roughly 35 Watts saved by moving away from fluorescent tubes and he’s got a great energy-saving hack. The LEDs used in the last aquarium light conversion were cooled by heat sinks and fans. We’d love to see this concept incorporated into that design.