Blog

An aquaponics solids filter removes uneaten feed and fish waste particles before they clog plant roots, pumps, and pipes. FAO’s aquaponics manual calls some level of mechanical filtration essential for healthy aquaponic tanks, and especially important for NFT and raft (DWC) systems. For small systems, FAO recommends a clarifier or mechanical separator, such as a swirl filter, which can remove up to 60% of removable solids. Size it at about one-sixth of the fish tank volume, or 10–30% depending on stocking density. Media beds act as their own filter at low stocking but need a separate solids filter above about 20 kg of fish per 1,000 liters (about 0.17 lb per gallon).

An aquaponics biofilter is the component that houses the nitrifying bacteria that convert toxic ammonia and nitrite from fish waste into nitrate for plants. Media bed systems don’t need a separate one, because FAO’s aquaponics manual says the grow beds themselves are excellent biofilters. NFT and raft (DWC) systems do need one. FAO’s sizing rule is based on daily feed: about 1 liter of volcanic gravel or 0.5 liter of Bioballs per gram of fish feed per day, with the biofilter container at least one-sixth of the fish tank volume. Bigger is safer: FAO says an oversized biofilter can’t harm the system and has saved many from collapse.

A DIY PVC NFT system (nutrient film technique) runs a thin stream of nutrient solution down sloped channels while plant roots sit in net cups above. A homemade NFT system built from PVC is a cheap, expandable way to grow lettuce, herbs, and other leafy greens. The core parts are rectangular or round channels, net cups, a small submersible pump, a reservoir, and return plumbing. The key design rules are a gentle slope, a shallow flow, and pipe that is safe for food crops.

To choose an aquaponics pump size , start with turnover: FAO’s aquaponics manual says densely stocked systems should cycle the total water volume about twice per hour, while lightly stocked systems need only once per hour. So a system holding 264 gallons (1,000 liters) needs roughly 264–528 gallons per hour (GPH) of actual flow. Then check that the pump delivers that flow at your head height, the vertical lift from the pump to the highest outlet. FAO’s small-scale designs use about 2,000 liters/hour (about 530 GPH) at about 5 feet (1.5 m) of head, which takes a submersible pump drawing roughly 25–50 watts.

An aquaponics greenhouse lets you grow year-round in cold US climates by trapping solar heat and keeping water warmer and more stable. FAO’s aquaponics manual notes greenhouses aren’t essential for small systems but are especially useful in cooler regions, where they can keep water warm through the cold months. The trade-offs are cost, the need for fans and ventilation to prevent overheating and high humidity, and more pest pressure. A good layout puts fish tanks in shade or the north side, grow beds where light is best, and covers water surfaces to control humidity.

Aquaponics winter growing is possible in cold US climates if you either keep the water warm enough for your fish or switch to cold-tolerant fish and crops. FAO’s aquaponics manual lists three strategies: protect and heat the system (insulation, greenhouses, passive solar heating), switch to cold-water fish and winter vegetables when average temperatures stay below about 59°F (15°C) for more than three months, or harvest everything and shut down until spring. Nitrifying bacteria slow down below 63°F (17°C), so in winter you also need to feed less and watch ammonia and nitrite more closely.

The best aquaponics water temperature for most systems is a compromise of about 64–86°F (18–30°C), the range FAO’s aquaponics manual gives for fish, plants, and bacteria together. Within that, match fish and crops to your climate. Warm-water fish such as tilapia, carp, and catfish, plus nitrifying bacteria, thrive at about 72–84°F (22–29°C), alongside crops like basil and okra. Lettuce, Swiss chard, and cucumbers prefer cooler 64–79°F (18–26°C) water, and trout won’t tolerate water above about 64°F (18°C). Bacteria slow down below 63°F (17°C), so cold water also means slower nitrification.

Aquaponics iron deficiency is the most common nutrient problem in aquaponics because fish feed contains less iron than plants need. It shows as yellow new leaves with green veins. The fix is chelated iron, not iron sulfate, because plain iron precipitates out of solution at the pH most aquaponics systems run. FAO’s aquaponics manual recommends adding chelated iron to about 2 mg/liter, and 1–2 mg/liter during the first three months of a new system. Match the chelate to pH: research in HortScience notes Fe-EDTA holds iron to about pH 6.5, Fe-DTPA to about 7.5, and Fe-EDDHA to about 9.

Aquaponics plants turning yellow usually points to one of four causes: iron deficiency, pH drift, low nitrogen in a young or understocked system, or root problems. The location of the yellowing is the fastest clue. FAO’s aquaponics manual notes that nitrogen deficiency yellows older leaves first, because plants move nitrogen to new growth, while iron deficiency yellows new leaves first, because iron can’t move within the plant. If nitrate is high but new leaves are yellow, FAO recommends adding chelated iron and checking pH. Keep pH around 6–7, the compromise range FAO gives for fish, plants, and bacteria.

Is tilapia legal in your state? Often yes, but with conditions. Tilapia aren’t native to the US, so many states treat them as exotic or restricted species. Some states allow hobby aquaponics with certain tilapia species and no permit, others require a permit, and some limit tilapia to specific areas or ban some species. Texas, Florida, and California, three of the most-asked-about states, each handle tilapia differently. Check with your state fish and wildlife agency before buying fingerlings.