Just this very day broke out my ancient air conditioning unit from the garage. I keep the fish tank room chilled on the few days a year it’s needed in the UK. Happy tank, happy people
I have a tank that runs hot even after changing every internal pump in the system. I added a chiller and haven’t looked back keeping the tank temp +/- 1 degree. My chiller kicks on about 1 time an hour during the summer for about 15 minutes and considerably less in the winter. We keep the temp in the house during the summer at a constant 23c degrees. Without the chiller the tank runs at just about 29c degrees.
Obvious statement of the day:
Depends on where the tank is located.
If it's in a (human) living area, you'll likely want comfortable temperatures there for people anyway, so I voted AC.