Your all Paranoid!
I have a 55 gallon Black rain barrel and it's buried in the ground with next to never direct sunlight exposure,the water temp never exceeds 70 degrees,I change the water once every three weeks,but over time the eels will change to a lighter color.
If you keep your eels in the basement,garage,back yard,out side next to your garage,or in your friggin attic the water temp will eventually come to ambient temperatures,thats just the law of physics that is,unless you become a total bitch slave and change the ice,water or turn on your chiller to keep them @ a temporary cool temp.but you also keep in mind as the water get's warmer there gonna die because oxygen will become compromised,A river,lake,pond,brook ect.is the best way to keep these things alive with out color change or weight loss.
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