I am not EMG, but I do keep endler's livebearers. They can be kept without a heater--but one of the advantages of having a heater is a stable temperature. I keep my endler's at about 76 and they do really well. I have talked to my LFS (Uncle Ned's Fish Factory in Millis, MA, one of the best) and they recommend heaters for most fish primarily for the issue of stable temps. If you keep your house at the same temp all the time, I don't think it would be a problem, but we turn our temp down to 60 at night and weekdays when noone is home. That's a pretty drastic temp shift in a small tank.
The only tank I don't heat is my newts tank, where the temp stays about 70 year round.
Jackie
The only tank I don't heat is my newts tank, where the temp stays about 70 year round.
Jackie