A shrimp jar is the most forgiving version of a closed ecosystem. Shrimp produce little waste, eat biofilm that grows anyway, and tolerate the temperature swings of a small volume better than most fish. The whole build takes an afternoon. The waiting takes longer.
This is the build I would give to a friend: a 2–4 litre glass jar, a handful of plants, two or three cherry shrimp, and one snail.
What you need
- A clear glass jar, 2–4 litres, with a wide opening. A mason jar, apothecary jar, or large pickling jar works. Avoid narrow-necked bottles for a first attempt.
- Dechlorinator. Tap water contains chlorine or chloramine; both will kill shrimp.
- A small bag of aquarium gravel or a fine sand. Avoid sharp gravel if you plan to keep shrimp.
- Plants: a golf ball of Java moss, one small anubias, and a stem or two of hornwort. More plant mass is better than more animals.
- Two or three cherry shrimp and one ramshorn snail. Buy from a local shop or a hobbyist, not from a jar that has been sitting on a shelf for weeks.
- A clean bucket or jug for preparing water. Never use soap on anything that touches the jar.
- A lamp or a bright window that does not get direct sun.
You do not need a filter, a heater, or an air pump for this build. If your room drops below about 18 °C in winter, a small heater is worth considering, but most homes are fine.
1. Clean the jar without soap
Rinse the jar with warm water and a clean cloth. If there is a sticker, remove it with a little cooking oil, then wash the oil away with water. Do not use dish soap, bleach, or glass cleaner. Residue is very hard to rinse out and shrimp are sensitive to it.
Rinse the gravel until the water runs clear. This can take several minutes; cloudy gravel will make the jar cloudy for days.
2. Add substrate and hardscape
Put 2–3 cm of gravel or sand in the bottom. Slope it so one side is deeper than the other; this gives the jar a sense of depth and gives plants a place to root. If you have a small piece of driftwood or a few smooth stones, add them now. Rinse them first.
Do not bury the anubias rhizome. The thick horizontal stem should sit above the substrate, or the plant will rot. Tie it to a stone with cotton thread if you need to. The thread will dissolve in a few weeks.
3. Plant
Fill the jar about one-third with prepared water so the plants stay wet while you work.
- Java moss: place it on a stone or a piece of wood. It does not need soil.
- Anubias: tuck the roots into a gap in the hardscape. Keep the rhizome exposed.
- Hornwort: let it float, or weight the bottom with a small stone. It feeds from the water column rather than the substrate.
Leave the front of the jar open. You will want to see the shrimp.
4. Fill with water
Fill the rest of the jar slowly, pouring onto your hand or a plate so the substrate does not cloud. Leave 2–3 cm of air at the top. Add dechlorinator according to the bottle, using the full volume of the jar.
Do not use distilled water. Shrimp need the minerals in ordinary water. If your tap water is very hard, a mix of tap and filtered water is usually better than pure distilled.
5. Let it run without animals
This is the part people skip. Put the jar in its place, set the light to 8 hours a day, and leave it alone for one to two weeks. The plants settle. Bacteria colonise the surfaces. The water may go slightly cloudy and then clear.
You are not “cycling” the jar in the same way as a filtered aquarium, but you are giving the biofilm time to establish. Shrimp graze on that film. A brand-new jar with no film is a hungry jar.
If the water goes green in this period, shorten the light to six hours and wait. If it stays green, do a 30% water change and shorten the light again. Do not add animals to fix an algae problem.
6. Add the shrimp
Float the bag in the jar for 20–30 minutes to equalise temperature. Then add a little jar water to the bag, wait ten minutes, and repeat. Net the shrimp into the jar; do not pour the shop water in.
Two or three cherry shrimp are enough for a 2–4 litre jar. Add one ramshorn snail if you want algae control. Do not add fish.
For the first week, do not feed. The shrimp will eat biofilm. If they look thin after a week, add one small pinch of shrimp food and remove what is not eaten after a few hours.
7. The first month
Expect changes. The water may cloud for a day or two after the shrimp arrive. A little algae may appear on the glass. The plants may melt back before they grow. None of this is necessarily a crisis.
Do a 20–30% water change once a week for the first month, using dechlorinated water at roughly room temperature. Top up evaporation with plain dechlorinated water. Keep the light period steady.
After a month, if the jar is clear and the shrimp are active, you can reduce water changes to every two or three weeks. If the jar is stable, you may not need them at all.
What “self-sustaining” really means
A shrimp jar is self-sustaining in the sense that it does not need a filter or daily feeding. It is not maintenance-free. You still top up water, trim plants, and remove excess algae. The jar runs on light and biofilm, but it runs better with a little attention.
The most common mistake is adding more animals because the jar looks empty. Resist it. The jar will look fuller in two months, when the plants have grown and the shrimp have settled. The second most common mistake is feeding too much. A shrimp jar needs very little food, and uneaten food is the fastest route to an algae bloom.
If you want to rehearse the balance first, the Pondlet jar lets you add plants and shrimp and watch the same relationships over simulated days. It will not teach you to clean a real jar, but it will teach you what overstocking feels like.