I know it's advised to get a heater and I understand why however, I've had him for 5 months now without a heater and for 4 of those five, he's made bubble nests and swam around happily. He's had a wonderful appetite and he's very attentive.
Could it be he was cold when he started acting funny and later developed fin rot?
When that happened, he had also been moved to a different spot in the room. He's back on my desk now and he seems great! Trust me, I've been watching closely.
I guess I'm just trying to ask if a heater is really a necessity.