CB,
Not being familiar with your project nor an aquaculture specialist this may sound like a silly question but, what is the goal of getting the nitrogen cycle going in the tank? Is this for assymilating fish waste?
Rainman was right on with the bacteria, Nitrosomonas can live in temps as low as 49 F but are most active in 70-85 F. They may be a bit slower in 65F water but certainly not dead.
If you are not using pond water in the tank, then what is your water source, a well? Tap water has residual chlorine in it which bacteria are VERY sensitive to. If you are using tap water, you need to aerate it for 24 hours before use. Also, I'm assuming your aerating your tank as well right? Did you seed your tank with bacteria? Do you have a carbon source? Once you convert from ammonia to nitrate, then what?...water changes, or denitrification?
