It’s interesting to notice the response is similar to others I heard.Pygmaeus, hastatus, and habrosus are 3 of the exceptions for corydoras stocking.
The absolute minimum is 5 gal for a single shoal of 6 WITHOUT other fish in the tank. If in a community, they need a 10 gal standard, meaning not a tall tank. It needs a longer footprint. They are active, but are small. Your tank is a 9, a touch on the small side for a community but your stock is fine and its got a nice footprint to allow swim space for pygmies .
Now if you turned around and wanted to put corydoras aeneus in there, id tell you no you need a 20 gal or larger. Because theyre way too large for anything smaller.
As for the pygmies, they have a very small bioload. Cories in general are pretty good on bioload to be honest, but the pygmies even more so.
Ive asked Planet Catfish the limits of a 10 gallon for pygmies. I got told 10-15 pygmaeus could be housed in a 10. I started with 7 and there was definitely more than enough space for 3 more. I have 10 and personally feel i could have more if they decided to breed on me.
Your guppies will be your largest fish in the tank. And they use all levels of it. Theyre larger, just as active (if not more!), and have a much higher bioload than all of your other fish. If your guppies are fine in the 10, so is a shoal of pygmy cories.
Now, since a 20 is the smallest limit for all cories, im going to go find me a bearded corydoras shoal and shove them in there....
(A) “you can’t do that”
(B) “Oh ok. I would love to understand why”
(A) ....
...
I got it a lot before coming here.
I absolutely agree with what your saying and this was my thought process while stocking
