All of the Aqualog books are excellent value, although they are not particularly cheap. They are full to the brim with first class colour photographs and to reproduce these in a book is an expensive process. Whether they are about Corydoras or some other species of fish they are the most comprehensive identification books you can buy. They never become dated because as new fish become available to the aquarist trade the books are updated.
They will not tell you how to set up a tank or what plants or rockwork you need. They will not tell you which filter to use or what type of substrate. They are a fish identification encyclopaedia and nothing more. But for those aquarists who are particularly interested in a particular species they are indispensable.