Originally Posted by Vsandme
Depends on the nano...if you get a biocube or similar it comes WITH all the proper filter, lighting, and as far as heating the lights take care of that so its self sustaining mostly
I think a lot of this depends on the climate you live in. For me, my lights can hold the tank around 80degrees during the day, but temps drop a lot at night if I don't run a heater. It's not so much the temp that can stress fish/corals as much as it is the fluctuation. A heater helps maintain a more constant temp.
IMO, a heater is necessary in all tanks.