Closed Aquatic Ecosystem

This aquarium is not technically completely closed. I made a decision not to cork it shut so gases can still be exchanged with the air. However, otherwise it is completely self sustaining except for the evaporation of water which requires the occasional top off. Completely self sustaining ecosystems do not really exist in nature. It's kind of like trying to create perpetual motion in physics. If you cork aquarium shut, it will only last so long. You may have seen those ecosphere things in stores that are completely closed. But, even they will die off after a couple years.

You will need:
Glass carboy
Substrate for designed for a planted aquarium
Water treatment (if you use tap)
Plants
Shrimp
Snails (optional)

Rinse off your substrate. Add it to the glass carboy. Fill the glass carboy with water. You can either buy purified water at a store, or add dechlorination stuff to your tapwater. Then add your plants. If the plants float, use a long stick or similar object to plant the plant roots in the substrate. No worries if the water is murky for a little bit. Placement of the aquatic ecosystem is crucial. What you're going for is something called filtered sunlight. Your aquarium should be near or next to a window, but not near a window that gets direct sunlight during many hours the day. This will lead to a fluctuating temperature that will kill shrimp and snails. Now, leave your ecosystem be for one week.

Your aquatic ecosystem is now ready for larger organisms. However, it will never be ready for fish. Without water changes and food, this sort of aquarium will need to be hundreds of gallons just to support a single fish. Shrimp and snails both eat algae, which is produced by sunlight. Start with just two or three shrimp. I bought cherry shrimps from my local aquarium. Later, when algae seems to be out of the shrimp's control, you can buy some snails. Make sure to add water after evaporation.