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Apr 21, 2013
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Hey, this is my first post so I am not sure how everything runs.
In my biology class we were given the assignment to basically make a self sustaining ecosystem in a sealed of container. It is a nightmare. In order to keep everything running we obviously need plants to convert co2 to oxygen. To keep them alive we need to water them, that's where the freshwater aquarium comes in. We would connect it with some sort of wick to water the plants.
Next to convert oxygen back to CO2 we need animals. So why not fish if we already need an aquarium? I've done some research and found it wouldn't be hard to set up a fruit fly culture to feed the fish.
What kinds of fish can I buy at a pet store that will eat fruit flies, be inexpensive, and be hardy enough to live in less than perfect conditions. I don't want to pick just any fish and accidentally torture it because I am not an expert in this subject by any means. Also what kind of fish/critters can I put in that would limit the build up of waste and bacteria (I don't want to get the fish sick.)
Difficult if not impossible to do with fish long term. They produce quite a bit of waste. The waste can be converted by bacteria and consumed by plants and algae.
Here's a company that does this with shrimp and I've read posts from people that have had these continue for a great many years. This might be more along the lines of something sustainable.
Generally speaking the systems we create are not actually closed systems because we as aquarists have our hands in them doing water changes, feeding, etc.
I make homemade biospheres at my home in a glass gallon wine/cider jug with a cup of pond water, hornwort, java moss and 3 snails. There are plenty of microorganisms in the pond water to get the system established and algae in the pond water gives everything something to eat. They're super simple and completely closed, I just pop the cap on them when I am done setting them up. You can put 2 shrimp in if you really want to, but there is a risk that you'll kill them because it's hard to get it right the first time. I fill the jug with same temp water from the tap (its safe with no chlorine or other chemicals) *** Only to where the jug starts to bottle neck*** It is very important that there is a good amount of air space above the water. Set it near a shady window so it doesn't overheat and kill all your critters and there you go. Snails clean the algae, produce waste, microorganisms you introduced with the pond water process it into nutrients for the plants, plants and algae provide food and living space for the creatures and oxygen. I have 4? at home right now and they're all approaching 2 years old. They have natural cycles with the populations of creatures in them and the snails don't usually breed because the environment is too small. You can stick a stick in there for decoration, sand and substrate is important because it gives bacteria something to live in. When you go to get pond water make sure you get some mud in there too, lots of things live in the mud and its the only way to be sure you've gotten something good.
Aquariums can't be closed systems because there is always exchange, be it air, water or food, besides there is no way to really completely close off that sort of container unless you calked your fish in. :C
I always thought that there is no such thing as a completely closed ecosystem that can sustain itself except microbial ecosystems that live in the deepest caves. Every ecosystem other than those get some influence from the rest of the world. Whether it be air or wind, or nutrients or even sand blown in from a far of dessert. I like silenthawks biospheres but he said that he pops the top on the bottles so there is air exchange from the outside world. I really have no idea what I am talking about, I just watch a lot of nature documentaries. A lot of them!
Good luck on your project! It sounds like fun but I am glad I don't have it!
Even those in caves are not completely closed as they obtain nutrients from above through seepage and insects etc.
Clarification on my terminology, popping the top on them I meant that the lid IS on. Otherwise the only outside influence is energy from sunlight.
The system will likely be affected by ambient temperature as well.
Sunlight and ambient air temperatures aside, it's a closed system so for sure you could try that. you could even try it without water. Grow some algae in a high humidity container, be it a box, a bottle, whatever. a little soil, some basic plant life (the algae or cress for example, not watercress though, that needs a good flow of water and is - believe it or not - demanding to grow) and a snail or two. It'd certainly last for at least a month if kept properly. You could even just work on a fruitfly culture in a sealed container but that's where it gets tricky in that, the fruit flies are a bit particular about their food. 
If it was me, I'd do something along the lines of Silenthawk's aquatic snails in a bottle idea.
I think the OP means self sustaining as in the food originates inside the aquarium.

Tek oot.
That's what I gathered. Food grown and waste processed all inside.

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