07-24-2012, 01:14 PM
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Generally, corys should be in groups of five or more, of a species. However, with more than one species, you can have less of each species. But more is always best--all of these fish naturally live in groups of hundreds of one species, and it is rare to find more than one species together. But that doesn't mean they won't live together in the aquarium; in their habitat, evolution has determined distinct species, sometimes one in each stream.
In a 29g, only considering the corys for the moment, I would have from 5/6 up to 10/12. No less than 3 of each species if possible. I have observed in my group of over 30 corys in the 115g that some species do prefer being together more than some others.