Yeah we're west of the mountains. I loooooove the wet spot, i actually sell some of my fish there when my local petsptore can't buy from me. So yeah, I guess i've got soft water
Then you have numerous options for a 20-21g tank of smallish fish.
You could do a geographic tank, say a SE Asian pond/stream with one of the dwarf species of rasbora (in Boraras genus), one or more of the small gourami (Chocolate, Licorice, pygmy, eyespot...), with crypts, floating Water Sprite for plants. Or an Amazonian pool with pencilfish, dwarf cory species, pygmy chain sword, floating pennywort pants. Or a Killifish setup with Central African killies [none in our profiles yet, but some members do have these].
Or you could do a theme tank, say a forest lagoon, with some of the aforementioned small fish but not paying attention to geography when it comes to fish and plants, just water/environment similarities.
The possibilities are endless.

And The Wet Spot has almost all of these fish in stock, when they are in season. Being wild caught, most of these fish are seasonal according to the collection times in their respective countries.
Byron.