I've been very happy with Reef Crystals. Although I can't image that there is much difference between the IO and Reef Crystals since they are both from Aquarium Systems.
http://www.aquariumsystems.com/salts.htm
Emperator is correct, you don't necessarily need a chiller. Given your canopies 12" height and open back, a couple fans should be sufficient to dissapte the heat from the metal halide fixture.
If you do find it necessary to cool down the temperature of your tank water you can open up the top...
