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When aquaponics fish not eating becomes a problem, the cause is usually water temperature, water quality or stress, not the food itself. Check these in order: water temperature (most fish eat less when water drops below their comfort range), ammonia and nitrite (should be near zero), dissolved oxygen (above 5 mg/L), pH (about 6.8–7.4), recent stress (new fish, handling, loud noise, a power cut) and signs of disease. Fix the underlying problem first, then offer small amounts of fresh feed once or twice a day and remove anything uneaten after 5–10 minutes.

When aquaponics nitrate too high readings show up, it usually means the system has more fish and feed than plants to use the nitrogen. Most aquaponics systems run well with nitrate (NO3) between about 5 and 150 mg/L. Levels above about 150–200 mg/L can stress sensitive fish, push plants toward soft, leafy growth with poor fruiting, and signal that solids are breaking down in the system. Fix it by adding plant growing area or fast-growing leafy crops, doing partial water changes, trimming feed or fish numbers, and cleaning out trapped solids.

An aquaponics nitrite spike happens when nitrite (NO2) climbs above about 0.5–1 mg/L because the second group of nitrifying bacteria hasn’t caught up with ammonia conversion. Nitrite causes “brown blood disease,” which stops fish blood from carrying oxygen. The fast fix is to stop feeding, increase aeration, do a 25–50% water change, and add plain salt (sodium chloride) so chloride is at least 6 times the nitrite level, because chloride blocks nitrite uptake at the gills. Keep salt doses low in aquaponics, since plants are sensitive to sodium and chloride.

An aquaponics ammonia spike means total ammonia nitrogen (TAN) has climbed above about 1 mg/L (ppm) and keeps rising, which can burn fish gills within hours, especially at high pH and warm temperatures. Emergency steps: stop feeding, add aeration, test pH and temperature, remove any dead fish or rotting feed, and do a 25–50% water change with dechlorinated water at the same temperature. Then find the cause, which is usually overfeeding, too many fish for the biofilter, a dead fish, low oxygen, low pH or alkalinity, or something that killed the nitrifying bacteria.

An aquaponics power outage is dangerous mainly because aeration and water circulation stop, so dissolved oxygen in the fish tank can fall to lethal levels within one to a few hours in warm, heavily stocked systems. Your plan should do four things: keep air going to the fish (battery air pump, inverter or generator), stop feeding, keep plant roots from drying out, and restart the system slowly and safely when power returns. A battery-backup air pump that switches on automatically is the cheapest and most important single item.

To size an aquaponics air pump , match the pump’s airflow to your total water volume and fish load, and make sure its pressure rating beats the depth of your deepest air stone. Many hobby growers start with roughly 1 liter per minute (LPM) of air for every 10–20 gallons of total system water for lightly stocked systems, and double that for heavier fish loads or warm water. A 300-gallon IBC system, for example, usually runs well on a 30–60 LPM linear or diaphragm pump feeding stones in the fish tank, sump and raft beds.

Healthy aquaponics dissolved oxygen levels are at least 5 mg/L (5 ppm) in the fish tank and throughout the system, with 6–8 mg/L better for trout, high stocking densities and fast plant growth. Below about 4 mg/L most warm-water fish such as tilapia eat less and grow slowly; below 2–3 mg/L they gasp at the surface and can die within hours. Nitrifying bacteria and plant roots also need oxygen, so low aquaponics dissolved oxygen shows up as ammonia spikes and root rot as well as stressed fish.

Semi-hydroponics with LECA (lightweight expanded clay aggregate, or clay pebbles) means growing houseplants in inert clay balls instead of soil, with a shallow reservoir of dilute nutrient solution at the bottom of the pot. The clay wicks water up to the roots while the gaps between pebbles keep plenty of air around them. LECA suits many popular houseplants, including pothos, philodendron, monstera, hoya, and peace lily. Success depends on fully rinsing soil off the roots, keeping the water level low, and feeding with a weak, complete fertilizer.

To size greenhouse heating for hydroponics, multiply the total exposed surface area of the greenhouse (walls, ends and roof, not the floor) by the temperature difference you need to hold on the coldest night and by the heat loss factor (U-value) of the covering: BTU/hr = area × ΔT × U. A double-poly greenhouse has a U-value of about 0.7, so a 12 by 20 foot hobby house with about 900 square feet of surface, held at 55°F when it’s 15°F outside, needs roughly 900 × 40 × 0.7 ≈ 25,000 BTU/hr of heater output. Add 10–25% for wind, leaks and distribution losses, and size by output, not input.