The most common way to kill shrimp in a jar is not neglect. It is food.
Cherry shrimp are grazers. In a mature jar they spend most of their day eating biofilm, algae, and decaying plant matter. That film is always growing. A jar with healthy plants and a little light produces enough food for a small shrimp population without any added food at all.
Feeding is something you do for a reason, not as a daily ritual.
What shrimp eat
- Biofilm: the thin layer of bacteria, algae, and organic matter on every surface. This is the main food.
- Algae: softer types, especially on glass and plants.
- Decaying plant matter: dead leaves and stems, as they break down.
- Prepared food: shrimp pellets, blanched vegetables, and powdered foods, in small amounts.
Shrimp are not fussy, but they are small. A single pellet can be a day's food for several shrimp.
How often to feed
In a well-established jar with plants and a mature biofilm, feed once or twice a week at most, and only if the shrimp look active and the jar is stable. In a new jar, do not feed for the first week or two.
A useful test: drop in one small piece of food and watch. If it is gone within a few hours, the shrimp were hungry. If it is still there the next day, you fed too much. Remove what is left.
How much
A portion about the size of a grain of rice per ten shrimp is a reasonable starting point for prepared food. For a jar with two or three shrimp, that is a very small pinch.
Blanched vegetables (zucchini, spinach, carrot) should be removed after 12–24 hours. They foul the water quickly in a small volume.
Signs of overfeeding
- Cloudy or milky water after feeding.
- A film on the water surface.
- Algae growing faster than usual.
- Planaria or detritus worms appearing.
- Shrimp gathering at the surface, which can indicate low oxygen.
- An ammonia smell.
If you see these signs, stop feeding for a week, do a 20–30% water change, and remove any uneaten food. Do not add a filter to fix it.
Signs of underfeeding
Underfeeding is less common and less dangerous. Signs include:
- Shrimp that look thin or have a sunken back.
- Very little grazing activity.
- No new molts over a long period.
- A jar with no visible biofilm (rare in a planted jar).
If the jar is mature and the shrimp look thin, increase the frequency slightly, not the portion. Feed twice a week instead of once.
Vacation and absence
A planted jar with shrimp can go one to two weeks without food, especially if there is biofilm and algae. Before leaving:
- Do a partial water change.
- Remove any uneaten food.
- Set the light on a timer.
- Do not add extra food “for the trip.”
If you will be away longer, ask someone to feed once a week, with pre-portioned food. More jars are harmed by overfeeding during a holiday than by the holiday itself.
Minerals and molting
Shrimp molt as they grow. They need calcium and other minerals from the water. If your water is very soft, molting problems can appear: white rings on the shell, failed molts, or deaths. A small amount of a shrimp mineral supplement, or a piece of cuttlebone, can help. Do not add more than the jar needs; minerals accumulate.
Food and the nitrogen cycle
Every piece of food that is not eaten becomes waste. In a jar, that waste becomes nutrients, and nutrients feed algae. Feeding is therefore a direct input into the algae problem. The less you feed, the more stable the jar.
This is the opposite of the instinct most people have when they see shrimp. The jar is not a pet bowl. It is a small ecosystem, and the shrimp are already eating.
If you want to see what overfeeding does without risking a real jar, the Pondlet simulation tracks food, detritus, and algae separately. Add food a few days in a row and watch the water respond.