00:00In winter, guppy death rates rise noticeably, but not because of the cold itself, as most keepers
00:06assume. A fish living in water that's 24 degrees Celsius during the day and drops to 18 degrees
00:12Celsius at night is at greater risk of dying than a fish living steadily at 18 degrees Celsius the
00:18whole time. Guppies are tropical fish, and their ideal temperature range is between 24 and 26
00:24degrees Celsius. In winter, especially in unheated tanks, water temperature drops with the night cold
00:31and rises slightly during the day, depending on room temperature. This swing can reach a difference
00:36of 4 to 6 degrees within just 24 hours. Here's the paradox no one really explains. A guppy's body
00:43can actually tolerate cold down to 18 degrees Celsius for extended periods. The problem isn't
00:49the cold. It's the speed of change. Studies in fish physiology suggest that rapid temperature shifts
00:56disrupt the process of thermoregulation and weaken the immune system for several days after each
01:02fluctuation. The result? The fish doesn't die from the cold directly. It dies a week or two later from
01:08a fungal infection or fin rot that its body could have resisted if the temperature had stayed stable.
01:14The solution isn't just raising the temperature, it's stabilizing it. A heater rated at about 5 watts
01:21per liter of water is usually enough for most home tanks, and setting it to 25 degrees Celsius
01:26completely prevents nighttime fluctuation. If you can't use a heater, a simple step like covering
01:32part of the tank at night noticeably reduces heat loss. So when you lose a guppy in winter after days
01:38of normal cold, the real cause is usually not the cold itself. It's the fluctuation. Those of you
01:44with a tank and no heater have you noticed a clear difference in fish behavior between night and day?
01:49Share your observations with me.
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