Mike I use a heavy duty dark gray barrel w/ a lid for my eels and they still turn lighter over time.
I have to change my water daily but mine's outside and it gets too warm even in the shade..
To make it easier to change the water I drilled like 5 or six holes about 6" from the top of my barrel for the water to drain thru.. My lid has a hole thats big enough for the air hoses and the garden hose to pass thru. I just stick in the hose and push it to the bottom, turn it on and let it run till its clear ( like 10-15 minutes).
When it gets above 85 i have to add fresh/cold water twice a day or I start to lose eels.
the grass near the eel barrel is the greenest grass I have...
