Damsels, some clown fish stay small, some gobies, some angelfish. You're not going to want to stock it as full as you would have fresh water tank. Also you need to make sure that you keep up on replenishing with RO water when it evaporates. And such a small tank it's going to make a huge difference in the salinity. I would maybe do a pair of clownfish or a couple damsels and maybe one little Goby or something. If you're not going to start with damsels which are the hardiest I would start with adding some snails and crabs . Then it's not a big loss if they don't make it. Not going to want to put too much in such a small tank. Larger is much easier especially if you're inexperienced. That said if you're very dedicated you can have a successful Nano saltwater
