I had to buy a chiller for my reservoir; on my second grow I got a nasty case of root rot, which I never wanted to deal with again. I keep the water temp around 67-68. At that temp, bad stuff can't grow.
I use Great White michorrhizae powder (beneficial bacteria) just to be on the safe side, and I've been using Advanced Nutrients, but this time I've gone back to my old nutes, Future Harvest.