I watched the exact thing happen when I cycled my first tank. Same fish in the same rolls.
The eatee is doomed. The eaters are the most aggressive things you can find in the "less than the size of a quarter" catagory.
Run to the store, and WalMart has them, and get a fry net that hangs at the top of the tank. Lizard cages with vent openings all over it do well, too. Seclude it there.
However, this situation will not change until that fish is dead, regardless of the tank they're in, IMO.
Sorry..