Panda cories would be great, and they'd love your sand. you could probably do 6-10 pandas in your 20 long. And oh man, do they LOVE big groups! My bronze cories are wild, they've got a shoal of 9 in my 29 gallon. They are super adventurous :)
in aqadvisor, it put 10 panda cories and 10 betta females at 85% stocking as well. If i plug in the aquaclear 20 as your filter, it says you are waaay under filtered though. with the aquaclear 30, it still says you'd be under filtered. I'd definitely get a great filter, lots and lots of plants, 7-10 betta girls, and 6-8 pandas if you go that route ^-^
aqadvisor.com is the stocking calculator Jen and I are using to get this info btw :)
OH. also it's important to wait for your tank to mature after it's cycled for a few months. cories, particularly pandas, are easily stressed, and can die real easy in an immature tank.
I'm new to live bearers as well, but you might be alright with a few females in your tank too. Just be aware that if they come from a mixed tank, they're probably pregnant, and will have several batches of babies before they run out of sperm (live bearers can store sperm- isn't that crazy???)
Last edited by djembekah; 09-13-2012 at 05:26 PM.