Correct; the first issue is the Serpae Tetra. The info in the profile [click the shaded name] explains the problems so I won't repeat.
To the cory, I would not combine the pygmy species with Serpae. The "average" sized corys like the panda would probably be OK, but no fewer than 5. Although this species can attain close to 2 inches, it often doesn't [no idea why, but I have had them for years and they do not grow past 1.25 inches, when other cory species in the same tank do].
Physical space is one consideration when it comes to tank sizes for fish, and the other is water quality. The reason five Corydoras panda will work in a 10g, or that a Whiptail Catfish will also work, is first because they are not length swimmers. The Whiptail rarely swims at all, more of short spurts now and then (usually if another fish startles it), but primarily just grazing over surfaces with hops to another leaf or something. The corys are not distance swimmers, as for instance barbs or danio; corys swim continualloy, but they do so by browsing over every available surface. So physical space can be less. Which brings us to water quality. Live plants help enormously, and with both corys and whiptail plants should be in the tank, along with chunks of wood (both to provide that surface area they need for browsing). These fish are all surface browsers. In addition, regular water changes are essential. With good husbandry, these fish will be fine.
Which brings me back to the Serpae; this species really needs more room, it is quite the opposite of the above. It is a shoaling fish that will become very aggressive without sufficient fish in the group, and in small spaces aggression is usually increased.
Last edited by Byron; 11-03-2011 at 05:10 PM..