Make a Closed Aquatic Ecosystem

A closed aquatic ecosystem is similar to an aquarium, only it is closed to the outside world so that all the needs of life must be met by the plants and animals within the system. Most of the species suitable for such systems are not very large or colorful, so if your desire is for an ecosystem filled with all manner of fish and plant life, your best bet is a regular aquarium. However, if you’re interested in creating a maintenance-free aquatic world that can last for months or even years, then read on!


Getting the Right Materials, Plants, and Animals for your Ecosystem

  1. Decide how contained you want your ecosystem to be. The more sealed off from the outside world your aquatic ecosystem is, the more difficult it will be to create one that is self-sustaining[1]
    • Hermetically sealed systems are completely sealed off from the outside world. Plants and animals must be very small and few in number to survive.
    • Closed systems allow gas and air exchange (through, for instance, a sponge set in the opening). Gas exchange helps to regulate pH levels in the water, and allows for the removal of nitrogen and intake of carbon dioxide, making these systems easier to maintain.
    • Semi-closed systems require some maintenance. All closed systems will eventually fail. You can keep your system going longer by changing 50% of the water each month. This removes wastes and adds nutrients. If your system is in decline, change the water more frequently.
  2. Decide if you want a freshwater or marine system. Freshwater systems are much easier to setup and maintain. Marine systems are less stable, but do allow for more interesting animal life, such as starfish and anemones.[1]
  3. Acquire a clear glass or plastic jar to contain your ecosystem. Mason jars, plastic 2-liter bottles, pretzel jars, or 3 or 5 gallon carboys will all work, though for beginners, a smaller system is usually easier to maintain.
    • For sealed systems, look for a container with a tight-fitting lid. For closed systems, consider covering the opening with cheesecloth or plugging it with a sponge.[1]
  4. Find a substrate for the plants to grow in. You can buy substrate at the store, or collect mud from a pond (which has the advantage of already having many of the tiny creatures you need in it).[2] For clearer water, consider adding a layer of sand over the mud or substrate.
  5. Purchase aquatic gravel or take gravel from a pond. The gravel layer will provide a surface for a microbial community and act as a filter, trapping particulate matter as gravity draws the water down through the gravel.[3]
  6. Use filtered water, pond water, or aquarium water. Aquarium water or pond water is preferred, because they already contain the bacteria that your system will need.[4] If using filtered water, you will need to let it first sit for 24-72 hours to let the chlorine dissipate.
  7. Choose your plants or algae. Plants provide food and oxygen for your ecosystem. You want plants or algae that are hardy and fast growing. You can collect them from a pond or purchase them. Some plants to consider include:[1]
    • Hornwort (freshwater) – Very hardy. Needs moderate light.
    • Pond weed, or elodea (freshwater) – Hardy. Needs low light.
    • Willow moss (freshwater) – Less hardy. Prefers cooler temperatures.
    • Bladderwort (freshwater) – Delicate.
    • Caulerpa algae (marine) – Hardy to the point of being a pest.
    • Chain algae (marine) – Requires high calcium levels.
    • Bubble algae (marine) – Hardy to the point of being a pest.
  8. Choose your animals. Animals eat algae and other waste, keeping your ecosystem clean. They also produce the carbon dioxide the plants need to survive. Start with only one or two larger animals, or 10-20 hyalella.[5] WARNING: Fish are not well suited to closed ecosystems. If you get them, they will die.[1] The following animals are more appropriate:
    • Cherry shrimp (freshwater).[6]
    • Malaysian snail (freshwater).[1]
    • Hyalella (freshwater / marine depending on species).[2]
    • Copepods (freshwater / marine depending on species).[2]
    • Asterina starfish (marine).[1]
    • Aiptasia sea anemone (marine).[1]

Setting Up Your Aquatic Ecosystem

  1. Add the substrate (soil) to the bottom of the container. If using a container with a narrow opening, consider using a funnel avoid a mess.
  2. Plant your plants in the substrate. If they float after adding water, try placing more sand and gravel on top of them to keep them rooted.[7]
  3. Add a layer of sand and then a layer of gravel. Cover all the exposed soil, but be careful not to crush your plant. Together, the substrate, sand, and gravel should fill 10-25% of the container.[2]
  4. Add water. Remember, if using filtered water, be sure you have let it sit for 24-72 hours to allow chlorine to dissipate. The water should take up 50-75% of the container. Leave 10-25% for air.[2]
  5. Add animals. Before adding them, let them acclimate to the water temperature by floating the plastic bag they are in on the surface of the water for a few hours. Remember: start with only one or two shrimp or snails, or 10-20 hyalella. Too many animals will kill your ecosystem.[8]
  6. Seal the container. For a sealed container, it is best to use a screw on cap or cork, though plastic wrap and a rubber band will do if that is all you have. For a closed container (allows air exchange), try cheesecloth or a sponge plug.
  7. Place the ecosystem in filtered sunlight. It should be near a window, but not one that gets direct sunlight for many hours, as this will lead to temperature fluctuations that could kill off your snails or shrimp.[2] Shrimp, copepods, and snails do best between 68°F and 82°F. Your container should be cool to the touch, but not cold.[2]

Maintaining Your Aquatic Ecosystem

  1. Watch your ecosystem closely in the first few weeks to be sure it is in the right location. Too much or too little sunlight can kill your ecosystem.[2]
    • If your plants look unhealthy, try more sunlight.
    • If the water is getting cloudy or discolored, try more sunlight.
    • If you get algae, or your shrimp die on hot days, try less sunlight.
    • Be aware that seasonal changes may necessitate moving your ecosystem.
  2. Adjust the number of animals and plants as needed after the first few weeks. This is important to keep your ecosystem healthy, as you probably won’t achieve the exact right balance at first.
    • Add more snails or shrimp if algae is growing. It is important to keep algae in check or it may cover the walls of your container, blocking out sunlight and killing your ecosystem.
    • If the water becomes cloudy, it may mean you have too many shrimp or snails. Try adding more plants.
    • If your animals are dying, add more plants.
  3. Know when your ecosystem is finished. There is no sense in keeping your ecosystem around after it has failed, particularly since it may begin to smell. Here are some signs that you need to empty out the ecosystem and try again:[2]
    • A bad or sulfurous smell.
    • Strands of whitish bacterial growth.
    • Very few or no living animals.
    • Most of your plants are dead.

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