Pond & farm
Koi live in water you look after. Everything they eat comes back out as waste, and the water can only stay healthy if something deals with it. This section covers the water itself: how much there is, what feeds it, what fouls it and what cleans it.
The cycle in one picture
Every gram of waste in the game starts as food. Follow it round:
Koi eat a share of their weight each day, more when the water is warm. Food the koi don’t eat sinks and rots.
Koi breathe ammonia out through their gills straight away. What they don’t digest comes out as solids.
Bacteria living on every surface turn toxic ammonia into much safer nitrate. They need oxygen and warmth.
Nitrate builds up slowly. Solids settle as sludge, which rots back into ammonia and uses oxygen.
Water changes, plants, the vacuum and filters take it all back out. Algae eat nitrate too, and turn the water green.
This is the nitrogen cycle, the same one every real pond runs on. A pond with a healthy, mature colony of bacteria is called cycled.
The three water bars
The Care tab shows the water as three bars, like three tests from a pond kit. Together they make up the pond’s water score (Good, Tired, Poor, Foul): the worst bar decides it.
| Bar | Measured in | Comes from | Taken out by | Hurts the koi by |
|---|---|---|---|---|
| Ammonia | mg/L | Koi breathing it out, sludge rotting, dead fish | Bacteria; water changes | Fast. Burns gills: sickness, lost health, koi stop eating. Above 1 mg/L koi lose health every day. |
| Nitrate | mg/L | Bacteria converting ammonia | Water changes, plants, the mud of a fry pond, algae | Slowly. Slows growth, dulls colour and feeds algae. |
| Solids | index | Poo, uneaten food, leaves, dead algae | Filters, the vacuum, water changes | Cloudy water, sickness, oxygen used up as sludge rots. |
The Farm tab adds Green water (algae), the size of the bacteria colony and how busy it is, and filter dirt. Over the water, a pond tab shows 水 when that pond’s water is poor.
See Ammonia & nitrate and Solids & algae for the numbers.
Your ponds
Every pond is a body of water with its own size, depth and life. Pond sizes come from the capacity upgrades: each fish space is a fixed amount of water.
- Holding pond. Where a new farm’s tosai grow on. It used to be called the garden pond; any pond can be renamed in Upgrades.
- Show ponds. One more for every variety you research. Name them for what they hold, like “Tancho pond”.
- Breeding pond. Deep, with lots of water per fish, so the breeders stay calm and well.
- Fry pond. Shallow and earth-bottomed. It’s full of life, so it clears ammonia and nitrate better than any other pond, and green water there feeds the fry.
- Quarantine pond and filtration pond. Planned. See below.
From buckets to a filtration pond
Small koi make very little waste, so a new farm runs on the pond’s own bacteria and a few water changes. Waste grows with a koi’s weight, which grows with the cube of its length. By the time your first tosai are nisai and sansai, they make many times the waste, and the pond needs help.
| Stage | What you do | When you need it | |
|---|---|---|---|
| By hand | Water changes (10, 25 or 50%), vacuuming the sludge, plants, a Light portion when the water is struggling. | From day one | In the game |
| Pump and filter box | Sponge filter, bead filter, bead filter & UV. A pump pushes the water through media that catch solids and grow bacteria. | Usually year 2–3, as your first koi pass about 35–40 cm | In the game |
| Bigger feeders | Large hopper, big hopper, timer feeder. | When adults empty the small hopper in a few days | In the game |
| Pumps that cost energy | Running costs for pumps, air stones, UV and heaters. | Mid game | Planned |
| Bottom drain | A drain in the floor pulls sludge away before it rots. Needs the pond rebuilt. | Big koi, full ponds | Planned |
| Filtration pond | One shared pond of chambers that every linked pond drains through: settlement, media, plants, UV. | Late game | Planned |
| Heating | Winter covers, heaters and heat pumps with a thermostat. | Late game | Planned |
In this section
Litres, depth and surface area, and everything that scales with them.
Food & feedersHow much koi eat, the foods, portions and feeder sizes.
OxygenDissolved oxygen, air stones and placement.
Ammonia & nitrateThe nitrogen cycle, the bacteria colony and water changes.
Solids & algaeMurk, sludge, green water and what you see in the pond.
Filtration & pumpsFilters now, and the bottom drains and filtration pond to come.
Temperature & heatingWhat warmth does, and keeping a pond at a temperature you choose.
EnergyRunning costs for pumps, air and heat. Planned.