20g catfish

You mean other than cories and otos, right?

There are dwarf catfish like the Akysis vespa that Msjinkzd is selling (or was, anyway)...
 
you could go with pretty much any of the cories, and your size tank allows you to have a large enough group that they will feel comfortable. i'd go with at least 6 of the same type. the albinos are nice, my two tend to be more at the front of the tank than the emeralds or the barbatus i have in there (9 cories altogether in a 55 gal with other fish).
 
Depending on what else is in the tank you could have a small pleco like a Bristlenose.

Just be aware that it will take a fair chunk of tanks available bioload, so if the tank is already heavily stocked dont go there.

Otherwise some Cory species is your best option, dwarf ones if you already have a well stocked tank.

Ian
 
I would totally get some of the Akysis MsJinkzd is selling. I have seen them in person, and they are TOO CUTE! They have these fat little tummies, and each one looks a little different, like snowflakes.
Here is a link to her sale thread...http://www.aquariacentral.com/forums/showthread.php?t=225395
She also has habrosus cories, of which you could put a dozen in the bottom.
 
You could get tatia perugiae (oil/honeycomb cats).
honeycomb-tatia-2.jpg
 
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