Aquaponics, step by step

1. The nitrogen cycle

In aquaponics the same litre of water does two jobs: it feeds the plants and returns clean to the fish.

1. Fish and grow bed — A pump moves water from the tank through a bed of clay pebbles or gravel and back to the fish. For your first system choose a media bed.
2. Fish give off ammonia — Fish eat and excrete ammonia through their gills and waste. Ammonia is toxic to fish from as little as 1–2 mg/L.
3. Bacteria do the work — The first bacteria turn ammonia into nitrite, the second turn nitrite into nitrate. Nitrate is only slightly toxic to fish and is the main food for plants.
4. Plants clean the water — Plants take up nitrate, and the roots and the bed hold back particles of waste. The only loss is what the plants transpire: roughly 1–2 % a day.

Why: In a thousand-litre tank the ammonia from fish waste becomes poison within a few days. A grow bed of clay pebbles solves that: bacteria turn ammonia into nitrate, and nitrate is food for lettuce, chard and tomatoes.

• Bacteria like 17–30 °C (63–86 °F), pH 6–8, oxygen and a large surface. They are killed by chlorine or chloramine, soap, medicines and drying out.
• When something isn't right, think of the bacteria first: are they short of oxygen, warmth or the right pH?

2. How much fish, how much grow bed

The system is worked out from the feed the fish eat each day.

1. At most 10–15 kg — For beginners at most 10–15 kg of fish per 1,000 L of water (22–33 lb per 264 US gal).
2. How much fish eat — Fish eat roughly 1–2 % of their weight a day, less in cold water.
3. Bed from the feed — 1 m² of grow bed for leafy vegetables takes 40–50 g of fish feed a day. For tomatoes and cucumbers 50–80 g.
4. Pump and air — The pump turns over the whole tank once or twice an hour: for 1,000 L that is 1,000–2,000 L/h. An air pump of 20–50 L/min with an air stone.

Why: Feed is the source of nutrients for the plants, so it decides how much grow bed you need. More fish doesn't mean more vegetables, it means more risk: when the power goes on a summer night, an overstocked system runs out of oxygen in an hour or two.

• Example: a 1,000 L IBC, 12 kg of carp, feed 1.5 % = 180 g a day. For lettuce 180 ÷ 45 = 4 m² of bed (about 43 sq ft).
• Start with 10 kg of fish. FAO gives 20 kg per 1,000 L as the upper limit.

3. Building on an IBC tank · Locked

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4. Cycling without fish · Locked

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5. Water · Locked

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6. Safety and winter · Locked

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