That brooder is much too small,for any number of chicks, let alone eight. If you were to let your chicks out into a large space, like the garage floor or a bedroom, they would be racing all over the place. And if you were to let them out into the yard outdoors, you would see them run and take off flying.
That's how much space one to two-week old chicks would LIKE. But they should have at the very least 1.5 square feet per chick.
People are under the impression that since the chicks are such tiny little things they don't require much space. That is so wrong.
Toss the totes. Get some cardboard boxes and make a real brooder the chicks will be happy in.
Also the small space isn't allowing for the chicks to move out of the hot zone if they get too hot. The thermostatic outlet may give you a false sense of security, but it may be too warm or not warm enough in reality. Have you observed the chicks to see their behavior? Are they huddled together most of the time? Then it's too cold. Are they clinging to the sides or lying prostrate? Then it's too hot.
But get a bigger brooder ASAP!