Hello; This is likely one of those question that will draw a variety of answers based on opinions perhaps rather than actual experience. I have done the very thing you ask about a number of times for varying reasons. Ths basic answer has been that the fish survived quite well.
I have had the temp set at around 70 degrees F on purpose with adjustments made on the heater thermostat during several winters. It was a gradual cool down during the fall. I also have the temps get up into the 80's F during the summer as I do not run the whole house AC all the time.
I have also had times when the power was out for a few days and the tank temps got down to the mid 50's F. I was into light stocking during the last time it happened and lost no fish at all.
I had some tanks in a basement and simply had to wait to get more powerful heaters and had the temps hover in the high 60's F for a time. Again with no loss of fish that I could contribute to being cool. This meaning that I lost no more fish during these times and the times mentioned above than at any other times.
I suppose some consideration will depend on the species of fish involved. My take is that few native home ranges of fish never have cool peroids. I also have gathered from my studies of biology that invasive species considered to be troplical have turned out to have the capacity to deal with cooler climates well.
At any rate I have lowered the temps in tanks to around 70 degrees F during several winters with good results.
I have had the temp set at around 70 degrees F on purpose with adjustments made on the heater thermostat during several winters. It was a gradual cool down during the fall. I also have the temps get up into the 80's F during the summer as I do not run the whole house AC all the time.
I have also had times when the power was out for a few days and the tank temps got down to the mid 50's F. I was into light stocking during the last time it happened and lost no fish at all.
I had some tanks in a basement and simply had to wait to get more powerful heaters and had the temps hover in the high 60's F for a time. Again with no loss of fish that I could contribute to being cool. This meaning that I lost no more fish during these times and the times mentioned above than at any other times.
I suppose some consideration will depend on the species of fish involved. My take is that few native home ranges of fish never have cool peroids. I also have gathered from my studies of biology that invasive species considered to be troplical have turned out to have the capacity to deal with cooler climates well.
At any rate I have lowered the temps in tanks to around 70 degrees F during several winters with good results.
