Never Ever use detergents to clean your livewell!!!
Either let it dry, or if that isn't good enough, use baking soda to clean it.
Never let fish die and float "belly up" in your livewell, if one goes "belly up", put it on ice in the cooler immediatly!
The only thing I ever do to clean my livewell is to hose it out with the garden hose and sprayer nozzle.