There are a few key factors to know about cory fry and raising them. They do not need to be fed anything until they have completely absorbed their yolk sac. They do need very clean water. Also, in a net breeder trap they is a risk of other fish killing the fry by sucking out the yolk sac thought the mesh. I use only solid breeder traps which circulate tank water though them and back into the tank. I much prefer using a small tank for pulling and hatching eggs and for the initial raising stage. It makes getting them food and keeping the tank clean as a whistle easier. You need to remove uneaten food as it will rot, tiny fry get into it and die.
Fry food that I can suggest: BBS (live or frozen), cyclop-eeze (frozen best but FD can be used- not a cheap food), NLS growth- the teeny size, kensfish Premium Growth Meal #00.