Hi Justin,
Welcome to the forums, ( From me at least ). The salt water hobby is expensive, but is worth the money when you see the beauty that can come from the tank. The fish you would want to have in a 20 gallon tank are....
- Red Striped Goby
- Cave Transparent Goby
- Catalina Goby
- Neon Goby
- FireFish
- LongSpine Cardinal Fish
- Purple FireFish
The fish above are just some of the fish you can put in a 20 gallon long tank.
You can have corals here are a few species...
- Neon Pineapple Tree Coral
- Purple Passion Tree Coral
- Taro Tree Coral
- Evergreen Starburst Polyp
- Neon Green Palau
And in case you want anemones....
- Condy Anemone
- Haitian Reef Anemone
Anemones are filter feeders, so baby brine shrimp should be added for the anemones can eat. Remember Anemones sting.
Also what kind of filter are you planning on getting and also what are you planning on feeding them.
- Live Sand and Live Rock is almost a MUST in the marine aquarium.
It's ideal to keep a separate tank with salt water for water changes and to replace evaporated water.
- Hope this helps
---Alex