CPDs are pretty boring. I had some and they just used to hide in my floating plants and only come out to eat. Apparently they are known for being quite elusive.
The Danio erythromicron are gorgeous. I was looking at them a while back but they require harder water and so I didn't get any.
Seems odd food safe containers would cause harm. I am just throwing this out there but could it be something like BPA in the plastic causing problems? Apparently it is bad to heat plastic containers that container BPA above a certain temperature as I think it leeches out or something.