Are you breeding for fresh or salt water? If in salt no need to have a different tank, add a few mollies or guppies to the salt tank. This is a natural food source for your fish.
If you are looking just to feed other fish guppies are the best. (Mollies are subject to ich too much to breed) Regular guppies no fancy's just feeders here. A $1 worth will provide you with more than you need in a 10 gallon in a month....really.