What can I put into the tank to make a perfect mini ecosystem?

[Signus]

Triops, Sand, freshwater fairey shrimp....

You can allow the water to evap and when you add water the next time, there'll be eggs from the animals. Be warned, however, the plants will need to be emersable and surive dry spells.

 

[abh19]

Equilibrium

This is a fascinating topic. I read some of the other threads on this topic too...

As a biologist, I think it'd be cool to be able to have a self-systaining closed-system tank. I have kept some guppies in a closed system (inputting only light) for several months. But it wasn't a visually appealing setup, and I don't think the daphnia enjoyed the experiment nearly as much as the guppies and the algae did....

One of my goals as a fishkeeper is to try and make the tank as ecologically balanced as possible. From this perspective, I view the need for water changes as a bad thing -- as an indication that the balance is off. If you want a tank full of fish for display, with inadequate plants and scavengers, you have no choice, well, then you have to do frequent water changes unless you can get awesome filtration. I also like to see fish and plants reproducing themselves... I wouldn't consider it an "ecosystem" if this didn't happen.

In my opinion, it's better to have an ecologically balanced aquarium than a completely closed system--for several reasons. Closed systems will be problematic for many reasons. One is visual appeal; a nicely manicured rock garden rarely exists in nature without frequent human interference. And those few spots of beauty where everything does fall into place without the help of humans are not closed systems either... there are constantly birds, mammals, etc tramping through, as well as water flow, air flow, etc. Another of the problems with trying to assemble a self-sustaining system is size. The less species you have in a closed system, the more unstable it will be. Random events (death of a scavenger, large brood of consumers born) will cause big shifts and the system won't have the resources to balance them. Having a larger number of different species of organisms allows the system more ways to adjust itself and find a new equilibrium in response to any changes. In order to have a large number of species, you need a lot of space (or very small species!). Even the earth loses species at an estimated rate of several hundred per year (I think... if I recall the numbers correctly). And that was happening before the industrial revolution, so don't blame it on global warming! It's just a fact of life.

So, is it possible to have a perpetually reproducing and recycling closed-system aquarium? No, I don't think so. Possible to have a ecologically balanced self-sustaining aquarium that sometimes requires minimal intervention from humans (cleaning algae off the light source, de-clogging the filter intake) and which doesn't run forever but runs for a very long time? Yes, it should be.

Does anyone have any more experiences or ideas they've tried (that worked or didn't work) in regard to setting up an "ecosystem"... either in the areas of energy (plants/algae --> primary consumers --> secondary consumers, etc) or recycling waste products (scavengers)? Are some plants more more suited to an aquarium ecosystem than others?

 

[bkw1982]

There will always have to be maint on an aquarium, and the setup will determine the water changes and maint needed. A heavily planted tank will prob hav more maint then a lightly planted tank, and a heavy stocked tank more water changes vs a lightly stocked tank. i wouldnt go without a water change more then 2 weeks, even with a great filtration, just becuase things need to be replinshed in the water.

Out with the old, in with the new....change ur water or it'll smell like poo!!

 

[tinymitymo]

But.....
the reason we got started with our tanks was an ecosystem experiment my son did at school.

He came home with a two liter soda bottle with the top third cut off. In the bottom was gravel, a couple of stalks of anacharis, 3 snails and a pair of mosquito fish. The top third of the bottle had a piece of netting covering the narrow part, then dirt and then some seeds sprouting. This part was inverted with the narrow part down and put over top of the bottom part so that the water level was over top of the netted opening. On top of it all was another two liter bottle bottom loosely set inside the top to cap it off.

He brought it home in September and that thing sat in my kitchen window untouched by any of us until November. Then I worried that it would get too cold for the fish and we bought a 2.5g Eclipse Explorer tank and moved over the fish, plants, rocks and snails. We started feeding the fish then since we took away the dirt and plants.
At Christmas we got a 28 g tank and moved the fish again so give the 2.5 g to a betta.
One of the fish got huge and fat and then suddenly small again - yep, babies. The babies got eaten though and a little while later the female fish died.
The male is still going strong in our big tank though.

So was this a self contained eco-system or what? We certainly didn't feed the fish anything for three months and they were fine.

 

[Signus]

I think a major fact that we're all forgetting hear is that the amount of salts does not change, rainwater is practically distilled (there are still some particulate and acid forming compounds, but very minor.)

Anacharis isn't a great plant for fish to eat either. You're very correct about having as few fish/inverts as possible in a water volume. Hundreds of gallons of water pass through any given area in a stream per day, effectively diluting out any toxins.

So 29 gallons for a 2 or 3 small fish? Sure. You should still do water changes unless you have VERY accurate test kits.