He is in a 4 gallon tank. It doesn't take long to do a water change but I was worried about fluctuating the temp too much.
I'm just a bit over protective with him, he has been through so much recently. He managed to get ich/white spot, which led to fin rot. He finally started to look better last week and his fins are starting to regrow, then I noticed he was off his food yesterday and realised the temp was low. I have wrapped his tank in a blanket and put a desk lamp next to it which seems to keep it at about 74. I'll keep him in his tank for now and just keep an eye on his temp.
Thanks for the reply.