Hey Horsemanrocks,

For you or anybody who has resivoir temperture problems and don't have access to Hawain tap water, you might try a product by DutchMasters called "zone".
It will prevent root rot and other root pathogens and will allow for higher temps without damage.I used it while I was chasing the heat ghost in a NFT rez many years ago.

The other solution is to take a small (lunch box sized) styrofoam cooler, put a coil of your air line in it (from your air pump) and fill with ice. The lower you can get the air temp into the rez, the lower the rez temp will be.