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Solids & algae
Fish poo, uneaten food, leaves and dead algae are solids. They float at first, then settle on the floor as sludge, where they slowly rot. You can see all of it in the pond.
Murk and sludge
The Solids bar counts two things:
- Murk: solids floating in the water. It makes the water cloudy. Each day about % of it settles. Filters catch it before it can.
- Sludge: solids lying on the floor. It counts half as much on the bar, but it rots: about % a day at 22°C, less in the cold.
Solids = murk (mg/L) + ½ × sludge (mg/L)
Why sludge matters
Bacteria do break sludge down, but that isn’t a clean-up: rotting sludge frees ammonia ( g for every gram that rots) and uses oxygen ( g of oxygen per gram). The Farm tab shows it as Sludge rotting among the oxygen flows.
That’s why koi keepers take solids out rather than leaving them to rot. A pond full of sludge has more ammonia and less oxygen than its fish alone would explain.
Getting solids out
| Tool | Takes out | Notes |
|---|---|---|
| Vacuum In the game | A pond vacuum on the Care tab. It stirs a little up into the water as it goes. Then it’s days before it’s free again. | |
| Water change In the game | its share of the murk, and a little sludge | See Water changes. |
| Filters In the game | floating murk | Catch murk before it settles. They fill up and need rinsing or backwashing. See Filtration. |
| Net cover In the game | autumn leaves | Leaves that sink rot like any sludge. |
| Bottom drain Planned | sludge, every day | Pulls sludge off the floor before it can rot, to a settlement chamber. |
Green water
Algae is a 0–100% score for how green the water is. It grows on nitrate, warmth and sunlight, fastest in summer.
- Lily pads shade % of the water and lotus % (up to 40% in all), which slows algae.
- A UV clarifier (the top filter) kills % of it a day.
- Algae eat nitrate as they grow. When they die off in the cold, they add to the murk.
- The summer algae bloom event is bigger when nitrate is high, and small if you have UV.
- In the fry pond green water is a good thing: it’s food for fry, and they grow up to 15% faster in it.
What you see in the pond
| In the water | It means |
|---|---|
| Brown-grey haze over everything; fish lose their sharpness | Murk (floating solids) |
| Dark patches spreading from the corners and edges of the floor | Sludge |
| Green tint | Algae |
| White foam collecting at the edges | Ammonia above about 0.3 mg/L |
| Bright, shimmering light on the floor | Clean water (water score 85+) |