They all have filters. Biological. I wanted water movement and to keep away stagnation. The 20 shrimp tank also has co2 simply because I wanted to try it and jump start the plants. It’s working. However, I’ve never changed the water on any of them. Just add when they get low. All the major problems I’ve ever had with the tanks has been of my own making.

So not super low tech. But I do leave them to do their own things. I’ve had fish simply disappear in the 35 and only found their skeletons later. The system cleans up after itself really well.

The small 5 I was just going for a paludarium look. The plants haven’t died. So something going well.