I have the same system. I think 65 is a bit on the cold side, they say 68 is the ideal temperature. 72 is nothing to worry about, as long as you don't go much above that you will be alright. You can buy this reflective "quilted" insulation often used to wrap heating vents etc, and I have a piece cut that covers the top of each plant. It reflects the heat as well as insulates the pot from the heat coming from the lights. Its not too expensive and it also helps keep old leaves and debris out of your hydroton.

keylime