I went with a upper and lower res for my F&D lava rock budding system for several reasons. One of the reasons is where I'm at it gets 50 below zero at times and it's easier to keep the res at a proper temp if it's not sitting on the floor. I keep the res separated from the grow and I keep the room at 69 degrees F. I have never tested the res with a thermometer but I go by touch. Not warm but not cold, but to cold for a bath. I use the lower res so I can get away with using cheap timers for a 1/2 hour cycle. I use an electronic valve thats set to the head of the table, opposite the drain to water and it takes 20 minutes to fill the lower res and 10 minutes to fill the table. Another reason, among many, I'm starting to get blind spots in my retinas so I separated my grow from my work area. I know this has nothing to do with water temps but be sure you have a proper pair of shades when you are working around 1000/w lighting. Don't trust ordinary sun glasses.