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How to care for corydoras
Get a good-sized tank.
Corydoras are not very large fish, and generally don't need too much room. A 20-gallon tank should be plenty big enough for a small school of non-dwarf corydoras (6 fish).
Of course, if you consider adding more fish, whether corydoras or something else, you'll need a bigger tank. There is a traditional " rule of thumb " that suggests 1-gallon per inch of fish that you put in the tank.