Join Date: Dec 2010
Location: Ontario, Canada
A Betta, 4 tetras, cory and upsidedown catfish is overstocked. The upsidedown catfish can get to be 4"..most corys get to be at least 2(although I don't know what size you have) neons are small but I always count them at an inch-ish..even without the Betta you're kinda full.
Both corys and UDCatfish are social little guys and prefer to be in groups which you definitely don't have room for.
If you rehomed the tetras and the UDCatfish, you could get a few more corys and keep the betta in.
So, no..you can't add anything else. In fact, if I understand correctly, you have a betta in there already and have a divider?
Thats too much. Get the Betta his own 2G tank and definitely don't get another one for that 10G until you rehome some of your existing fish.