Are you feeding them rabbit pellets, or kitchen scraps or what? I'm no expert, but I think sometimes rabbit pellets can contain salt so you might check the ingredients on the bag. I don't think regular salt would be good for your worms.

Are you refering to the actual size of your worms, or the number of worms when you say your worms "don't seem to be growing much"?

I like to throw in a handful of garden soil in a new bin too.

Feeding the rabbit pellets ,I may switch to chicken laying mash or crumbles .I have thousands of babies ,I need fish bait size . JOHN

You don't have any good old kitchen scraps for them? Cantaloupe rinds, carrot peelings, coffee grounds, egg shells, etc?

you won't grow big worms on animal feed, in fact if you've got "red wrigglers", you won't grow big worms at all, it takes ages for Eisena F to get any real size ... if you have night crawlers, they'll get big eventually, but they need a varied diet of carbon rich organic material, not high protein feed .... and easy on the eggshells, too much calcium doesn't help, and they can only use minor amounts of fine shell for grit, they don't actually consume it

Bill