I agree. Somewhere between 74-76 should be good. I keep all my tanks right in the middle at 76, so there is a buffer for any fluctuations and everyone will still be comfortable. I don't think 74 would be a bad thing with a goldfish. Water can easily reach that temp outside in the summer.
74 should work, that way if the heater breaks then it will either raise slowly up to still manageable heat (as long as you detect it fast enough) or the heater breaks down by shutting off and it only goes down to your room temperature (70-72)
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