5th - 50L/10G tall hex tank
This one was the first tank I bought. I didn't know anything about anything and had in there: 5 mollies (3m 3f!), 2 angels, and 3 common plecs!!! My angels and 1 balloon molly passed on quickly (cycle...

) and that's what's got me to fishlore. I came here asking for help. Havne't looked back since!
It's had mollies only, then my man's fish (leopard pleco + 3 puffers), and now is home to my male betta alone.
It's got soooo much substrate it's a nightmare. 1 layer of earth, 1 layer of thin red gravel, 1 layer of slightly thicker blue gravel and 1 layer of pebbles. The pebbles are to prevent the betta from being stupid and swallowing the small gravel again (giving me a huge scare in the process). It also decreases the tank's depth as bettas are shallow water fish.
I love his tall rock ornament (and so does he). It's like it was custom-made for the tank. It's got a little hole in the middle that the betta loves to use to get to the other side. It's got a couple of flat platforms too. The idea was that he'd rest on it. Haven't seen him do that yet. I've put a clump of java moss on top so he can sleep on that at night. Again, am yet to see him do that.
He's also got some large marbles to keep him curious, as well as a long empty log. He loves to swim through that log.
He's very clever with his food basket too, and loves to play in the bubbles. He must be the only betta in the world to like water agitation. That's why I've left the bubble thing on full blow, as he really enjoys swimming against the current in that corner of the tank.
Oh, and he's totally in love with his plants. He's forever swimming through the leaves.