You can use crushed lettuce leaves, banana skins, or turnip slices. Use dechlorinated tap water. The water will turn pinkish and cloudy, but it will clear up later.
For 100 fry use about 2 pounds of infusoria daily.
You could also use liquid fry food, from what I've read. Not sure about the efficiency of it, though.
just a note, infurosia will not last fry for a "few weeks" they'll only be big enough fo rthem to eat in the first week of life. After a week, infurosia becomes too small and not nutrious enough for the babies.
Infurosia is a general term for tiny micorsopic organisms that grow naturally in your fish tank. Such as paramecia and all that kind of stuff. Fry will pick at it, but after a few days they become free swimming infurosia will not last.
That's one of the reasosn why i don't bother culturing inforusia, i just feed my fry mw (they can take it down as soon as they become free swimming). I keep java moss in there just and they can pick at the infurosia if they want to, but it's by no means a relied food soruce for me
On the other hands, i believe planarians are much better