so I was just thinking... what if you could leave a tank for months....
You had enough plants to eat the nutrients with just the right light level to keep them happy for months... you had maybe just a tiny bit of c02 injection barely any... maybe none at all... but you had A LOT of plants...
you had a couple fish... and some how you had a natural food source... maybe a ton of daphnia and just a few fish... so the daphnia could grow and reproduce faster then they were being eaten... is this possible? Is something possible like this? What could be food sources for the fish tho? Snails maybe? daphnia? you might need like a terrium... where flys could lay larva for food or something along those lines it seems? It would be really good to actually make a terrium and have a food chain naturally work so you rarely ever needed to clean or do anything to the tank... like a mini rainforest... + a filter... ? Anything ever done along those lines?
Planted tanks can supply a lot of food for certain fish. I think we often over-estimate what amounts of food our fish need. Sure they'll eat what you give them, but in nature things might be different, and who knows what a diet that is too rich and ample does to their health and lifespan.
I have left my tanks repeatedly alone for 4 weeks (vacations overseas) and coming back, all the livestock looked just as good as always.
Of course that doesn't work with all fish, and especially not with overstocked tanks. My examples: I have a 36gal tank with Endlers that I basically don't feed. They thrive and actually start to overpopulate (IMO) the tank. Endlers are a good example for fish that can find some food in well planted tanks without needing additional feeding.
Another example... I have two Yoyo loaches (oldtimers, 5 years old) that basically eat snails, cherry shrimp, blackworms, and whatever they find in a 100 gal tank. I do feed them once a week or so, but it wouldn't be absolutely necessary.
Another example... some African Butterfly fish, they don't need much food since they basically hang out all day without much activity. The female has figured out to catch all the Cherry shrimp that make it up to the surface. That's a good example where the supply of Cherries will never be affected, because these particular fish never leave the surface.
Algae eaters are good examples for fish that don't need attention. Otos of course, and Flying Fox/Ancistrus etc for larger tanks.
I don't think Daphnia would work too well... they don't have a way to get away, so fish just have a huge feast and it's over. Maybe if you could keep them in a separate compartment within the tank. Cherry shrimp are good in that respect, since they are not that easy to catch, and once they are grown up many fish don't consider them snacks anymore. Blackworms are a good example too.
In nature, fish often live in moving waters. Or in lakes where the population density is very low. Water changes are not that unnatural...
So, if you have a relatively large and/or relatively understocked tank, you can make that work. Let the plants and shrimp/snails establish first, then add selected fish that won't upset the balance.
Consider an automatic water change setup so you don't have to interfere. Fertilizers can be dosed automatically over relatively long times. CO2, if pressurized, can sit for a year or longer without the need to mess with it. If light levels are relatively low, and you choose slower growing plants, there isn't that much work to prune them back.
That way you can have minimum maintenance, and call it eco or natural or whatever you want, and still have a nice-looking tank and healthy fish. Of course it takes some discipline not to overstock.