bottom-eater suggestions? (to be housed with Convict pair in a 20G)

a gravel vaccuum is your best bet. the only catfish i could recommend for that sized tank would be cories, and they would not have much of a chance against a breeding pair of convicts. any plecos you put in there, even a small species, will just poop out any leftover food it eats, which will make the sand look even messier. don't overfeed, and clean the bottom yourself.
 
Agreed not to add a BD to the con tank, cons would have a field day with there new toy. The last snails i tried to add to my con tank didnt make it to the bottom.
 
frick. so what about diversity. can i add some ghost shrimp or snails? what about a crayfish?
None. Either the crayfish attack your fish or the fish get their gourmet meal.;) Latter can be said on shrimps and snails.
 
AquariaCentral.com