My first tank (aside from an unfiltered 2.5gal goldfish tank) was a 5gal metal framed tank that I kept with live plants and livebearers and tetras. Undergravel filter and lighting was a fluorescent desk lamp lol...
Mine was a 125gl I traded my brother for a car payment. He was in a real bind. I had a irredecent cat fish, green terror, and a bunch of tin foil barbs.
55 gallon with red eared slider......... then later filled it up added a fluval 304 (as well as undergravel) and changed to a 10 year olds version of a predator tank with 5 jaguar cichlids and some lima shovelnose and 3 needlefish
20g with about 20 african cichlids, a corie cat, a bulldog pleco, and some other fish (can't remember what else was in it since this was 10+ years ago)