I used the publix around the corner from me until I bought my ro
unit. can't beat 30 cents a gallon lol. I woudl strongly urge you to use a di
as well though.
The list for corals and inverts is so huge that you can do!
Have you checked out Aquarium Fish: Tropical Freshwater Fish and Saltwater Fish for Home Aquariums
It has the requirements for most any invert, fish and coral you can think of.
I have in my 4g pico mostly corals, a candycane, lots of zooas, mushrooms, a duncan, an acan, xenia, a kenya tree (wouldnt recommend that one, it spreads like the plague). I also have a clown goby and peppermint shrimp, emerald crabs, a pom pom crab and a porcelain crab.
in your size tank you could easily add a fire shrimp or a cleaner shrimp. You could also get a clown fish and maybe a small goby.