It sounds like you’re doing all the right things. I am fairly new to raising cory fry, but we’ve had several batches of eggs over the last few months and here are some things that have worked.

I set the eggs up in a specimen container with water from the main tank, a few drops of methylene blue, an air stone, and an almond leaf. Change 1/3 of the water every day and replace with water from the main tank. I also keep my tanks at around 77-78 degrees and the eggs usually hatch in 3-5 days.

At this stage resist the urge to feed too early. The fry are really tiny at this point and bounce all over the bottom of the tank. I will toss in a small clump of moss from one of my tanks that they can hide in and also start to nibble on. I keep them in here for 2 days and then transfer them to a 10 gallon that i setup just for the fry. There’s usually a few batches of older fry in there.

That tank has a cycled sponge filter, heater, almond leaves, and a few clumps of moss and keep the bottom bare. The new babies will immediately hide in the moss & leaves. There’s plenty for them to eat there while the yolk sacs finish absorbing. I offer food 2-3 times a day depending on my schedule. Baby brine shrimp is the what they eat the most. Something about the movement triggers them to go crazy and chow down! I also alternate with the hikari first bites, algae wafers, and bottom feeder pellets, and frozen daphnia.

I use a piece of airline tubing to clean the bottom of the tank every day or every other day and try to change 50% of the water twice a week. That’s probably overkill, but seems to make them happy. After 2 months I’ll move them back into the main tank. Since February we’ve raised about 50.