I make my stocks in a slow cooker using either a whole chicken or a mix of wings and necks or whatever mammal bones I have. I get at least a few inches of jello every time. The first time I didn't know what to expect so I though I'd done something wrong haha. It may be the dilution because I usually get a thick layer of jello and a thin layer at the bottom of liquid.
I also second the baking soda. If you aren't worried about 100% natural, bar keepers friend is cleaning pixie dust. I've never scratched anything with it so it should be fine for cooktops, especially ceramics.