I have a 100 gal rubbermaid tub in my basement which is the sump for my 180 display on the first floor above it. I would say my basement is in the low 60's as I have been closing off the heat vents. I have two large titanium heaters controlled on my apex to maintain tank temp. They hold the overall system tank proably +/- 1 degree at any time....in otherwords very stable.
The problems I have been wrestling with is humidity in the basement and the colder temps.... I have found condensation on plumbing pipes particularly the drains. This is causing some corrosion in some other interesting places too. To solve somewhat, I have basically turned off my furnace's humidifier to help dry out the air... and then opened up the heat registers and return vents. This is creating much more circulation in the basement. The temp of the basement has come up a bit as well....and I am seeing less condensation. Of course, this may then mean more top off being used. But.. it may be something to consider as you tweak your system.