Do platies and guppies need heater??
Guppies and Platies are both tropical fish and it is better that you have a heater. I myself have kept guppies in a coldwater tank in the summer without a heater and they only live for about 2-3 months maximum so i recommend that you get a heater. I know the two fish are very hardy and easy to take care of both that is mainly to do with the condition of the water and not so much of the temperature. Heaters are cheap any way so you might aswell get one so you dont get a fall in temperature overnight which will easily kill any tropical fish especially guppies because their small bodies can not function in the cold and when there has been a suddenly temperature fluctuation.