The idea of a completely self-sustaining ecosystem within an aquarium has interested aquarium hobbyists and fish keepers for many years. A self-sustaining aquarium is one where all the inhabitants can survive without the constant care of a person. Nothing goes in; nothing goes out. Ideally the only requirements from the outside would be light and the addition of extra water on occasion. Creating a perfectly self-sustaining ecosystem is an art, requiring checks and balances, a fair understanding of biology, and patience. The first aquarium you try may not be just right, but remember, the outdoors have many levels of ecology at work. The more complex you make your community, the simpler it becomes to maintain; thus it is the complexity that draws the intrigue of many.
What Do You Want From Your Aquarium?
There are many different ways to approach a self-sustaining aquarium, from a small fish bowl to a 200-gallon tank. Each comes with its own challenges and rewards.
- doesn't take up much space
- fast to set up
- little room for diversity and representation of all necessary levels of organisms
- less room for error
- nitrates build up faster
- plants outgrow the tank faster
Overall: a bowl is great for experimenting, but very challenging to keep self-sustaining for very long.
Medium-Sized Aquarium (10-30 Gallons)
- more space for plants to grow
- more options for diversity of organisms
- more chance for sustainability over time
- takes up modest space
- fairly easy to set up
- higher cost than a smaller set-up
- more substrate (sand and gravel) needed
- still not large enough for ideal sustainability over a long time
Overall, this is probably the best choice for the average hobbyist with only moderate space and a strong interest in developing a sustainable aquarium.
Large Aquarium (60-200+ Gallons)
- significant room for sustainability
- can handle multiple species of more complex organisms
- the highest chance of sustainable longevity
- heavy (with water weighing 8.35 pounds per gallon, a large aquarium including the glass and water can weigh over 1000 pounds)
- hard to make room for
- more expensive to light, heat, and set up
Overall, a large aquarium (100 gallons plus) has the best chance of sustainability over a long period of time, but it is so big and heavy that it's just not realistic for many people.
What You'll Need
Every aquarium needs a few basics to get started:
1. You need an aquarium; it could be a bowl, a large jar, a milk jug with the top cut off, a rubbermaid storage box or an aquarium designed specifically for fish, just something that lets light in and holds water.
2. You will need substrate, preferably a few types for maximum ecological diversity; this will include sand, gravel, and medium-sized rocks or river rocks.
3. Water, with or without dechlorinating drops
4. Plants. (We'll discuss what types of plants.)
5. Objects for decoration or hiding places. These could include, rocks, sticks, clay pots, PVC pipes, plastic plants, or store-bought decorations like a pirate skeleton or a treasure chest.
6. A light source. Overhead or room lighting just won't cut it, and placing your tank or bowl in direct sunlight can result in fish deaths. A fluorescent aquarium light is much better, to ensure the growth of algae and plants as well as to display the beauty of your aquarium.
7. Critters! (More below.)
Making your aquarium able to sustain itself isn't as simple as just pouring sand in the bottom, filling it with water, and tossing in a fish. It takes several steps to assure an established food chain and the survival of your aquarium on its own.
First you'll want to establish the substrate of your aquarium. I prefer to put in the finer substrates (for example, sand) as the bottom layer and then larger ones (for example pea gravel) on top as the next layer. This will give you a strong rooting base for your plants, and allow air pockets between the gravel for waste to settle, and build up a nutrient layer for your plants.
In medium to large aquariums, a substrate depth of 2 inches of sand and 1½-2 inches of pea gravel or other similarly sized coarse substrate should be adequate for optimal plant growth and waste capture.
In a smaller bowl or mini-aquarium, an inch of sand and 1/2 inch of coarse substrate should be enough to maintain a plant without taking up too much of the water space.
Now that you have your aquarium set up with substrate, it's time to add the water. You have two choices:
- use water from your tap plus dechlorinating drops
- use bottled spring water from the store
I prefer to use dechlorinating drops because the brand I use (API) also detoxifies heavy metals in the water.
The food chain is the most important aspect of a sustainable ecosystem. In smaller aquariums the food chain won't reach much complexity beyond an algae-based food source, but in larger setups a variety of species that feed on algae, plants, and even other fish may be incorporated.
For a tank's food chain to be successful it has to be put together in the correct order. Each "link" of the chain must be adequate before the next link is introduced.
In a basic tank, algae and micro-organisms are going to be the foundation of the food chain. To encourage their growth. you'll need a bright fluorescent light and something to get them started, i like to use a small amount of fish food flakes mixed into the water to start the process. A good way to encourage the growth of algae is to mix some water from an existing fish bowl or aquarium into your new one. The nitrates from the fish waste will become fertilizer for the algae.
This brings us to our next step: plants. There is no hope of having a self-sustaining aquarium without plants, because plants use the waste produced by the fish as fertilizer. Not only do plants improve water quality, but also they compete with algae for nitrates, controlling those algal blooms that make your tank a murky green mess.
There is a lot of thought that must go into which plants to use in your aquarium. Some things to consider are:
- the rate of growth of the plant (which determines wheteher you'll constantly have to trim and manage it)
- the size of the plant,
- whether it is edible for fish and snails, and
- which part of the aquarium it will grow in (from the ground up, from the surface down, floating, growing on branches or rocks)
For a diverse and more successful aquarium, a variety of different types of plants should be used. Here are some ideas for each layer of the tank:
- Bottom: hair grass, corkscrew grass, green rotala
- Branches and rocks: Christmas moss, phoenix moss, Java moss, crystalwort
- Surface: duckweed, lotus
The final step once the plants and algae are established is to introduce the moving parts: the animals.
This is really a two-part step, and even a three-part step in larger aquariums.
First you'll need to add micro-critters. These can range from something tiny like micro-planarians and daphnia to small pond snails. These will be the base of the food chain for any fish that eat more than just plants or algae.
After enough time has passed for these little guys to become established and start reproducing, it is time to add the next link in your food chain. For small fish bowls, I would recommend only herbivorous species like freshwater shrimp, because there isn't enough space for adequate populations of any higher levels in the food chain to thrive. For any size aquarium I would recommend any of the freshwater shrimp species; ghost and red cherry shrimp are the hardiest and probably least expensive.
For a larger aquarium you can add some variety to the food chain. I would recommend starting slowly with predator species, and only adding more as the populations of food organisms grow.