Interactive lesson

Feeding fish and water, step by step

Interactive lesson: first you feed the water, then the fish — natural food, the Secchi disc, oxygen at dawn, grain by temperature, lime, manure and winter.

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The whole lesson as text

1. First you feed the water

In a carp pond the fish don't live on grain. They live on the water.

Sun feeds the algae — Sun and nutrients from silt, manure and fish waste feed tiny algae. The water turns greenish.
Algae feed tiny crustaceans — Algae feed water fleas (daphnia) and other tiny crustaceans. They and the larvae are the main food of fry and a large part of carp food.
Silt on the bottom — The silt is home to worms and larvae that carp and tench dig out. Don't scrape the bottom bare every year.
Grain is an extra — With grain the fish make better use of the protein from natural food. For 1 kg of carp growth you need roughly 3–4 kg of grain.

Why: Grain gives energy, while the protein comes from natural food. A pond with healthy, greenish water and a rich bottom gives twice as much fish as a pond with clear, empty water, on the same grain.

A pond needs sun, silt and moderate nutrients. Don't keep it in the shade.
An extensive pond without feeding lives on this chain alone and gives 2–4 kg of fish per 100 m².

2. Read the water

The colour and transparency of the water tell you whether there is food and whether an oxygen shortage threatens.

Make a Secchi disc — A round disc 20 cm (8 in) across, in four quarters, white and black alternating. A cord through the middle marked every 10 cm, with a weight under the disc.
Lower it in the shade — Lower it into the water in the shade, around noon, until the disc disappears from view. The depth on the cord is the transparency.
Read the number — Greenish water and 30–60 cm is healthy plankton. Below 25 cm there are too many algae: no manure, less grain, fresh water, aerator at night.
pH and ammonia — pH for carp 6.5–8.5, weekly in summer, morning and afternoon. A high afternoon pH with ammonia can be dangerous even if the morning reading is fine.

Why: Water that feeds can also kill. Too many algae use up oxygen at night, and the fish die at dawn. A thermometer, a Secchi disc and a pH drop test kit are enough for a small pond.

Blue-green scum and a rotten smell are cyanobacteria: no swimming, don't let livestock or dogs drink, let in fresh water.
For a trout tank and aquaponics add tests for ammonia and nitrite and, if possible, an oxygen meter.