Cloudy water is the most common jar problem, and the least useful thing to panic about. Different kinds of cloudiness have different causes, and most of them are temporary. The mistake is treating all of them the same way: a big water change, a filter, or a chemical clarifier usually makes a new jar worse.
First, look at the colour. Then decide.
White or milky cloudiness
A new jar often goes milky in the first week. This is usually a bacterial bloom: dissolved organic matter from the substrate, plants, or tap water feeds a sudden population of bacteria, and the water looks like weak milk.
It is not dangerous in itself. It usually clears on its own in a few days to two weeks as the bacterial community settles and the jar finds a balance.
What helps:
- Wait. Do not add chemicals.
- Keep the light period steady.
- Make sure the jar is not overfed. In a new jar, there should be no food at all for the first week.
- A small water change (20%) if the cloudiness is very dense or lasts more than two weeks.
What does not help: changing all the water, scrubbing everything, or adding a filter to a jar that was designed without one. Each of those resets the bacterial community and can make the bloom come back.
Green water
Green water is a free-floating algae bloom. The water looks like pea soup, often within a day or two of a change in light or nutrients.
The cause is almost always an imbalance between light, nutrients, and plant mass:
- Too much light, especially direct sun.
- Too many nutrients, usually from overfeeding or a disturbed substrate.
- Not enough actively growing plants to compete with the algae.
What helps, in order:
- Reduce the light to six hours a day for two weeks. If the jar gets direct sun, move it.
- Stop feeding for a week.
- Do a 30% water change and gently remove any visible algae.
- Add fast-growing plants such as hornwort or water sprite if there is room.
Green water often clears suddenly when the balance tips back. A jar that has been green for a month usually has a nutrient source that has not been removed: decaying plant matter, uneaten food, or a substrate that was disturbed.
Brown or tea-coloured water
Brown water usually comes from driftwood, leaves, or a substrate that releases tannins. Tannins are not harmful; in fact, many shrimp keepers use them deliberately. They lower the pH slightly and give the water an amber tone.
If you do not want the colour, remove the wood or boil it before use. If you like the look, leave it. Do not try to filter it out with charcoal unless you are prepared to replace the charcoal regularly.
A sudden brown tint with a bad smell is different. That is decay. Remove the dead plant or food, do a water change, and check for a dead animal.
Particles and dust
Fine particles that never settle are usually substrate dust from an unrinsed gravel, or floc from a bacterial bloom. They are harmless but ugly.
Rinse new substrate until the water runs clear before adding it. If particles appear later, a gentle siphon during a water change will remove most of them. Do not stir the substrate; that releases more dust and nutrients.
What not to do
- Do not change all the water. A full change removes the biology you are trying to establish.
- Do not clean the glass and the substrate and the plants all at once. You will remove the biofilm the shrimp eat.
- Do not add a filter to a jar that is cycling. The jar does not have a cycled filter to preserve; the surfaces are the filter. A small air-driven sponge filter can help a heavily stocked jar, but it is not a fix for overstocking.
- Do not use algaecides in a shrimp jar. They are hard to dose in small volumes and can kill invertebrates.
A simple decision tree
Milky white, new jar: wait, reduce feeding, keep light steady.
Green, established jar: reduce light, stop feeding, 30% water change, add plants.
Brown, with wood or leaves: likely tannins, no action needed.
Brown, with a bad smell: remove decay, water change, check animals.
Particles: siphon gently, avoid stirring.
Cloudy after a water change: likely mineral precipitate or disturbed substrate. Wait a day. If it persists, check that you used dechlorinated water at room temperature.
When cloudiness is a symptom
Cloudiness is often the first visible sign of a problem that is better measured another way. If the water is green, the nutrients are probably high. If it is milky after feeding, too much food is going in. If it is brown after a plant dies, the plant was adding waste rather than removing it.
The Pondlet simulation shows clarity, nutrients, and algae as separate values, which makes the relationship easier to see. In a real jar, you have to infer it from the water. The inference is most of the skill.