Unlike most other hydro growers, I don’t bother trying to control water temps. In most cases my buckets/totes sit on the floor of my grow tent, which is directly on a concrete basement floor. In the dog days of August, my water temps get up to the 24C range. In winter they have generally been too cold (as low as 54F). Last winter I did use aquarium heaters to get my water temps up. I feel like that really helped me out when I got to flower in my deep winter grow last year. This year I am using a much bigger reservoir and I have a radiant heater right next to it, so my water temps have been around 18-19C.
I have grown plants in 3 gallon and 5 gallon buckets and 8, 14, and 17 gallon totes. I got root rot in the 8 gallon totes (similar to those Under Current style buckets). In that particular case I had a single 2" air stone (being supplied air from a 935gph air pump with a six size manifold on it). Once I doubled up the air stones (after a thorough cleaning and pruning away of infected roots) I solved that problem.
In general if I’m somewhere between 60-75F I don’t sweat it at all and haven’t had any real serious problems. I would only bother tackling water temp issues as a last resort (personally), unless you have a couple hundred extra bucks to spend on a chiller.