My first tank was a 20-gallon hexagonal tank in 1993 that I spent all my babysitting money on. I had colonial hydroids in the tank which I had no idea what they were, and thought the little "jellyfish" (medusa stage) were simply awe-inspiring. I had a Sebae Clownfish, a Sebae Anemone, a Coral Banded Jerk (Shrimp), one piece of base rock, and a couple plastic corals. My highly sophisticated filtration included an undergravel filter with coral gravel, and I might have had a powerhead on one of the uptakes to improve filtration.
I did love the tank though. I think my mom has pics somewhere...