what best to feed ramshorn snails instead of the plants in my tank?

Howdy,

Even though red ramshorns are supposed to be more plant friendly than the
orange ones, 50 of them still reak havoc on many plant species since my
original pair started to make like they were on the Discovery Channel.

I have since moved them to a little covered tank with an over-the-side
filter away from my planted tank.

My question - what diet will get them grown and healthy the fastest so I can
trade them back at the pet store?

They like fish food, but I'm looking for a cheap alternative.

Any scientist types who have specific knowledge of %protein, %carbs, etc?

BTW, here's one thing that didn't work; they seemed especially fond of
ceropteris in the big tank, so I tossed all the surplus into their tank when
I did my pruning. They continued eating it, but it may have not been
nutritionally adequate. I had about 40% mortality in a few months.

They gobble up whole wheat bread crust and apple cores, but I have no clue
if that is nutritious.

There are lots of (chicken) egg shells in the tank for calcium or whatever
both shells are probably made of.

Regards,
Keith Loyd