They don't need them but I feel better knowing that their environment
is stable : ) I remember a story from another goldfish keeper who did
not use heaters in her tanks. She went on vacation in the heat of the
summer and while she was gone the house sitter turned on the air
conditioning. She arrived home to find all her fish had ich due to the
temp. change. Just to clarify, when I said I use heaters in all my
goldie tanks I meant in my fancy goldie tanks. I find my commons to be
much more hardy and do not use a heater in their tank.