Thank you for your concern! But to say goldfish don’t need a heater is a very general thing to say, and not totally accurate.
Goldfish thrive in temperatures ranging from 60-75F. They can tolerate lower temperatures in the winter, if healthy, and are like koi in that respect. However, their digestive system actually stops at temperatures around 50F. That is why you do not feed koi or goldfish during the winter, despite leaving them in the pond!
So, room temperature water is usually 60-75F but it can be a lot lower or hotter depending on where the tank is! My guys are in the basement, and I live in New England. The temperature is starting to get low here, especially in the basement (I mean it’s current 55F outside!). I have the big bin heated and tonight it’s finally cold enough for me to put a heater in the small bin as well, to ensure they don’t go below 60F. These fish are recovering from a severe internal parasite infestation, malnourishment, and ammonia burns. I want their bodies to be in the perfect environment for healing!