Copper works real well... but I would REALLY stay away from that one. Due to the heat exchange (or lack of it) you will have to find something with really thin walls to maximize an already poor heat conductor. Keeping the water filled hose submerged for a significant amount of time to realize any cooling effect makes me think you will either have to significantly slow your flow or lengthen your hose... if you were to do plastic or rubber.

You know if you were to build a turf scubber styled water overflow system with a fan over the exposed running water you would accomplish two things. First would be a lot of evaporative heat loss, the second would be... well, evaporation. But then each would require it's own sump to pool the water before sending it back to the QT tank.

Just thinking out loud here...