How to Set Up a Desktop Ecosystem

The short version

• A desktop ecosystem is a 1 to 3 gallon jar or vase of plants, moss, and a small invert cleanup crew that runs with no filter and no heater on a desk or shelf.
• The plants and the biofilm on every surface do the filtering; a colony of cherry shrimp (Neocaridina davidi) and a few snails graze the algae and leftover food.
• Stock inverts only. Under 2 gallons the water chemistry swings too hard for a fish, so this is a shrimp-and-snail build, not a betta bowl.
• Below: the jar, the plants, the cleanup crew, the build order, and the 5 minutes a week it still takes.

A desktop ecosystem is the smallest closed loop that actually holds: a wide-mouth jar with a few plants, a marimo, and ten shrimp, sitting in bright light near a window and running for a year on nothing but a weekly top-off. The trick is that nothing in it is decoration. The moss grows the biofilm the baby shrimp eat, the shrimp and snails turn leftover food back into plant fertilizer, and the plants pull the waste out of the water before it can build up.

What it is not is a fish tank. A 2-gallon jar has so little water that ammonia and temperature move faster than any fish can ride out, which is why this build is stocked with invertebrates instead. Get that one rule right and the rest is easy.

What a desktop ecosystem actually is

A desktop ecosystem is a nano, no-filter jar built the way a Walstad tank is, scaled down to 1 to 3 gallons and stocked only with shrimp and snails. The plants and the bacteria on every surface handle the filtration a motor would do in a bigger tank, so the jar runs silent with nothing plugged in but a small light.

The size is the whole constraint. A glass jar or vase in the 1 to 3 gallon range holds enough water to stay stable for inverts, but parameters swing hard under 2 gallons, so a 2 to 3 gallon jar is far more forgiving for a first try. More water is more buffer, so pick the biggest jar that fits the desk.

The jar, the light, and where it sits

Start with a wide-mouth glass jar or vase, 2 to 3 gallons if you can. The wide mouth matters more than the shape: it gives gas exchange at the surface and room to get your hand in to plant and prune.

Light is the one thing you plug in. A cheap nano clip-on LED runs the low-light plants a jar needs and goes on a timer for 6 to 8 hours a day. Do not solve lighting by parking the jar in direct sun: a sunny window cooks a small volume and feeds an algae bloom that outgrows your plants in a week. Bright indirect light near a window, plus the clip light, is the stable setup.

The plants that do the filtering

Weight the jar toward easy, low-light plants that grow without CO2. Three that carry a desktop ecosystem:

• Java moss (Taxiphyllum barbieri) is the backbone: it holds the biofilm baby shrimp graze, tolerates 64 to 82 F and pH 5.5 to 8.0, and asks for nothing but a place to attach. Tie it to a stone or let it drift.
• A marimo moss ball (Aegagropila linnaei) is not a moss but a ball of algae that shrimp pick at all day. Roll it over weekly so it keeps its round shape, and note it prefers cooler water, 59 to 77 F.
• A rhizome plant like java fern (Microsorum pteropus) adds height and pulls nutrients; it lives 68 to 82 F and stays nearly unkillable as long as you never bury the rhizome.

Plant heavily from the first day. The plants are the filter, so a sparse jar is an unfiltered jar with nothing doing the work.

The cleanup crew: shrimp and snails

The animals in a desktop ecosystem are the cleanup crew, and they are the reason it closes the loop. A colony of cherry shrimp (Neocaridina davidi) is the centerpiece: they max out at 1.2 inches, carry a very low bioload, and graze biofilm and leftover food off every surface. Start with 10, the minimum for a stable colony, and they will breed to fill the jar.

Two things keep shrimp alive. They need minerals in the water to molt, GH 4 to 14, so soft tap or RO water needs remineralizing. And copper kills them, so keep it out: it hides in some plant fertilizers and fish medications. A mature, planted jar with no copper source is the safe home.

Add a few snails to work the surfaces shrimp miss. A ramshorn (Planorbella sp.) or Malaysian trumpet snail (Melanoides tuberculata) eats detritus, and the trumpet burrows and aerates the substrate as it goes. Both self-limit to the food supply, so a population boom just means you are overfeeding.

Animal	Latin name	Adult size	Job
Cherry shrimp	Neocaridina davidi	1.2 in	Graze biofilm and leftover food
Ramshorn snail	Planorbella sp.	0.75 in	Eat detritus and soft algae
Malaysian trumpet snail	Melanoides tuberculata	1 in	Burrow and aerate the substrate

The build, step by step

1. Rinse the jar and the hardscape. No soap, ever: a trace of detergent kills shrimp. Rinse a stone or a piece of wood under hot water.
2. Add substrate. A thin half-inch of inert sand is enough for a moss-and-marimo jar. For rooted plants, cap about 1 inch of organic topsoil with a half-inch of sand, which feeds them for a year.
3. Plant it heavily. Tie java moss to a stone, drop in the marimo, anchor a java fern. Do this while the jar is only damp, before you fill it.
4. Fill slowly. Pour onto a saucer or your hand so you do not churn the substrate into a cloud. Use dechlorinated water.
5. Light on a timer, 6 to 8 hours. Then wait. Do not add a single shrimp yet.
6. Cycle for 3 to 6 weeks, then add the cleanup crew a few at a time.

The first month, and when it settles

A new jar is not ready for animals on day one, even a jar this small. It still cycles: the plants and the growing bacteria colony have to catch up to the waste the system makes before it is safe for shrimp. Give it 3 to 6 weeks.

The signal is the water test, not the calendar. A cheap liquid test kit that reads ammonia, nitrite, and nitrate is worth more than any guess: wait until ammonia and nitrite both read zero on two readings a few days apart before the first shrimp go in. In a heavily planted jar the plants often keep ammonia very low the whole way through, which is a good sign, not a reason to skip the test.

Add the crew slowly. Ten shrimp is a full starting colony for a 2 to 3 gallon jar; add two or three snails at the same time or a week later. Light and slow beats heavy and fast in a jar with no filter to cover a mistake.

What it still costs you every week

Self-sustaining means the biology filters and cycles on its own. It does not mean you never touch the jar. A desktop ecosystem still asks for about 5 minutes a week, and skipping that is where these jars fail.

The weekly work is small: top off evaporation with dechlorinated water (a small jar loses noticeable volume, and topping off with plain water concentrates minerals over time, so use fresh dechlorinated water), feed a tiny pinch every few days at most, and pull any dying leaves. Once a month, a small water change of 10 to 20 percent resets anything that has crept up.

The honest failure mode is stocking a fish. A betta or a couple of small fish in a 2-gallon jar looks fine for a month, then an ammonia spike from the higher bioload wipes it out, because there is no filter and too little water to absorb the load. The second failure is a copper source killing the shrimp overnight. Keep it inverts-only and copper-free and a desktop ecosystem will outlast almost any tank on the shelf.

Frequently asked questions

Can you keep fish in a desktop ecosystem?

Not in a jar under about 3 gallons. There is too little water to hold parameters steady and no filter to absorb the bioload a fish adds, so ammonia swings faster than a fish can tolerate. A desktop ecosystem is a shrimp-and-snail build. If you want fish, step up to a filtered or heavily planted 5 to 10 gallon tank instead.

How long before a desktop ecosystem is stable?

Plan on 3 to 6 weeks before any animal goes in. The jar has to cycle even at this size, and the way you know it is ready is a liquid test showing ammonia and nitrite both at zero, not a date on the calendar. Add the shrimp slowly once it clears.

Do you need a filter or a heater?

No, and that is the point of the build. A heavily planted jar filters itself through the plants and the biofilm, and shrimp and snails suit room-temperature water, so no heater is needed if the room stays roughly 65 to 78 F. A small light on a timer is the only thing plugged in.

What is the easiest cleanup crew to start with?

Ten cherry shrimp (Neocaridina davidi) plus two or three snails. Cherry shrimp are the beginner invert: hardy across GH 4 to 14, very low bioload, and they breed to fill the jar on their own. Add ramshorn or trumpet snails to work the substrate and glass.

Once the jar is stable, every choice that keeps it that way is a compatibility question: which shrimp suit your water, how many the volume holds, which plants grow under your light. Run the build through the build planner for a stocked, balanced starting point, check any animal against the compatibility database, and read the rest of the getting-started and build guides for the next step up. If you are choosing between this and a first tank, the best beginner aquarium setup and the first aquarium mistakes to avoid are the next two reads, and what a planted tank costs will tell you the budget.