Welcome aboard.
You can feed tadpoles fish food and some romaine would be good too. Now the problem I think you are going to run into is fish are quicker to eat than tadpoles are. So, keeping it well fed may be a problem. If the Jack Dempseys were adults the tadpole would be toast.
When an adult the bullfrog will need a large enclosure. A thirty gallon is just too small for an adult bullfrog. There is a thread here about a home made bullfrog enclosure. Check it out.