I agree with jag51186 that combining other substrate fish (= loaches) with corys is not a good idea. The corys might not have too much problem from their perspective, but the other fish (loaches) probably would, as you are dealing with very different temperaments. Loaches in general are hierarchical shoaling fish, meaning that they live in groups and form an hierarchy within the group, and they are territorial (corys are not) so any intruder into "their space" is usually not welcomed.
Most loach species get a decent size and as they need a group (they are highly social fish) this means lots of space for individual territories. You have two 20g tanks now, and are thinking of a 55g (from your other threads); the 20g are not suitable for loaches (other than the kuhlii type, and perhaps the hillstream type, though these latter require very specialized aquascapes), but the 55g might suit some loach species but again I would not include corys. Some of the common loaches in the genus Botia canget large, easily up to a foot and more, so if these are considered on their own when the 55g is in place, species have to be carefully selected.
Betta fish were mentioned...this is not a community fish, and will always be better on its own (male), or in a sorority which is another issue as jag mentioned.
Byron.
