My son put together this small one (12 gal). Built the “mountain” and “caves” from plastic and lava rock, the water is pulled in from the bottom and spills out the top), planted it, its more of a plant aquarium than a fish aquarium. We have cherry (tiny, like 1 cm) shrimp, clown EDIT they are kuhli loaches, snails - lot of bottom feeders to keep things clean. Only fish are a few tetras and guppies. The goal was a self-sustaining tank that doesn’t need much feeding or maintenance. It doesn’t have a filter that needs to be serviced. The floating duckweed is apparently good fish food. Gro LEDs above the tank so the plants have light.
I am thinking of adding a couple of small aquatic crabs. Will name one Harry and one Sally, so they can meet. Couple months in, the water quality stays perfect, the shrimp keep disappearing (do they eat each other? unclear) but the plants, creatures are otherwise thriving. Almost no maintenance. Just dechlorinate and add some water to replace evaporation. I do a tiny bit of feeding, mostly to see the creatures get active. Dry duckweed and grind it to small particles.
I wish there were more “land” so we could have semi-aquatic creatures, but oh well. I would also like to add a second bubbler, to move the water around more.
I had larger tanks (100 gal) when I was younger. All freshwater. They are fun, but I’m not into that much size or work now.