maybe insulate the resovoir somehow? i havent done hydro before but been looking into it and heard of people wrapping their res in 3-4in thick foam tryin to maintain temps, also at your hydro store (if yu have access to one) they should have some kind of high strength hydrogen peroxide. the kind you buy in a general store is i think 3% and the stuff at hydro shops is 30-35% instructions say 1-5 drops per 5 gallons a day it sterilizes your res and also adds dissolved oxygen to the root system and cleans your lines.