Taking care of your Corydoras

Food

There are an enormous amount of different foods you can use for your Corydoras. The best is of course to give them live food (i.e. mosquito larvae, newly hatched brine shrimp, and micro and grindal worms).
The second best is frozen food such as adult brine shrimp, cyclops, and red mosquito larvae. They are all kind of expensive (unless you grow you own worms such as grindal and micro) and most people I guess use commercial prepared food such as flakes and pellets.
You can also make your own food such as beefheart and shrimp mix. I will expand on that at a later time.
Home of the Rainbowfish, excelent site, with many types of live food
The Krib, almost all you need to know about food
The Krib, almost all you need to know about live food

Water change

Boring but necessary!
Clear water is not the same as good fish water. The eaten (and uneaten) food you put in the tank is converted to different "poisons" in the tank. To keep the levels down you need to change water regularly. Some of the more sensitive species might need half the volume to be changed every week, while others only need 10% every week.

Filter cleaning

Do like this to keep the good bacteria culture in the filter media when you clean it:

Fill two buckets about half ways with water FROM THE TANK. (NEVER use tap water since the chlorine/chloramine will kill off parts of the bacteria.)
Take out the sponge/filter media and squeeze it repeatedly in one bucket.
Move it to the other bucket and squeeze repeatedly again
Repeat with new buckets of clean water from the tank until the water in the bucket stays clean.
Put filter back into the tank/filter canister.
Fill up the tank.

No matter how large your filter is or what type of filter you use you NEED to change water! See Care for more discussions about water.

Diseases

If kept in an aquarium where you regularly change the water, have good filtration, and feed them well, most Corydoras are pretty hardy.

Will add more info later.