Aquaponics and Hydroponics: Growing Food Without Soil

By GoldBlock WorkshopPublished Updated

The short answer

Hydroponics grows plants with their roots in a nutrient solution instead of soil; aquaponics combines that with raising fish, using bacteria to turn fish waste into plant food. Illinois Extension names lettuce, kale, basil and cilantro as crops for a homemade passive hydroponic system. Both methods depend on water quality (NMSU gives the aquaponics targets) and, for most systems, on electricity for pumps and aeration; Oklahoma State University Extension says a backup power system should be installed where electricity is unreliable. In aquaponics, the University of Hawai’i’s food-safety guide says to rinse produce only in “potable water (never aquaponic system water or other irrigation water).”

Key numbers

Hydroponics: the simplest start

Illinois Extension describes hydroponics simply: “Plants are grown without soil and the roots are submerged in a liquid nutrient solution.” A small passive system (a tub of nutrient solution with plants floating in it) is enough to grow lettuce, which Illinois Extension calls “the easiest plant to grow in a homemade passive hydroponics setup,” along with kale, basil, cilantro and other greens.

What it needs, per Illinois Extension:

  • Light: unless a window is very sunny, add a shop light or grow lights kept a few inches above the plants.
  • Nutrient solution: mix a purchased concentrate with water at the label ratio, and change the water completely every two weeks.
  • Testing: check pH and electrical conductivity (EC) weekly; most plants do well at a pH of 5 to 6. If pH drifts too high or low, “the nutrients become unavailable to the plants.”
  • Water: avoid water from a water softener.

Aquaponics: fish, bacteria and plants together

New Mexico State University Extension defines aquaponics as “a method of food production that combines fish farming with soilless plant production.” NMSU describes the three living parts:

  1. Fish produce waste containing ammonia.
  2. Bacteria (nitrification) turn ammonia into nitrite and then nitrate; NMSU notes this requires oxygen, so low dissolved oxygen can stall the biofilter and let ammonia build up.
  3. Plants take up nitrate as fertilizer, which cleans the water for the fish.

Starting a system (cycling)

NMSU calls cycling “the essential first step in setting up any aquaponics system.” With fish, it takes about 4 to 6 weeks at low stocking and feeding, testing ammonia and nitrite daily; fishless cycling with pure ammonia (no perfumes, soaps or additives) takes about 10 days to 3 weeks. The system is ready when nitrates appear and ammonia and nitrite fall to 0.5 ppm or lower. Oklahoma State University Extension (HLA-6729, 2021): “Dechlorinate water for two to three days by letting water sit with consistent aeration.” The CDC: “You can also remove chlorine from water by letting it sit out for a few days. You cannot remove chloramine this way, however,” and “You can buy products at a pet store to remove chlorine or chloramine”; which disinfectant a utility uses is on its water quality report. OSU also notes that “15% to 20% die-off happens when new fish adjust to the system.”

Water quality targets (NMSU)

Measure Target
pH 6.4 to 7.4 (6.8 to 7.0 best)
Total ammonia nitrogen Under 1 ppm
Nitrite Toxic to fish at 5 ppm; keep at or below 1 ppm for tilapia
Nitrate 5 to 150 ppm
Dissolved oxygen 5 ppm or higher
Water temperature 65 to 85°F for warm-water systems generally; 81 to 84°F for tilapia (NMSU table). Cold-water fish such as trout need cooler water and more dissolved oxygen (NMSU: trout thrive at 55 to 65°F and need about 6.5 ppm dissolved oxygen); the target depends on the species

Power: the weak point

Oklahoma State Extension: “If electricity supply is unreliable, a backup power system should be installed.” Its outage stopgap: “Take water from the sump tank and pour into the fish tank” to restore oxygen temporarily, and “repeat this process every 1-2 hours until power returns.” Pumps, heaters and lights sit next to water. CPSC’s fact sheet on ground fault circuit interrupters says GFCI protection matters “especially for circuit outlets in particularly vulnerable areas such as where electrical equipment is near water,” and lists outdoor outlets among those the National Electrical Code has required GFCIs for since 1973 (CPSC: What Is A GFCI?); permanent wiring falls under the electrical code and a licensed electrician’s work. Open tanks and sumps are open water: the CPSC says “it takes only a few inches of water for a young child to drown” and “Young children can drown in even small amounts of liquid” (CPSC, September 27, 2012). Backup power for pumps is covered in backup power for vital loads.

Food safety with fish

The University of Hawai’i’s guide (written for commercial farms) and the CDC’s fish page give the rules below.

Common questions

What is the easiest thing to grow hydroponically?

Lettuce. Illinois Extension calls it the easiest plant for a homemade passive system, followed by greens and herbs like kale, basil and cilantro.

How long does it take to start an aquaponics system?

About 4 to 6 weeks to cycle with fish, or about 10 days to 3 weeks fishless with pure ammonia, before the bacteria are established (NMSU Extension).

What happens to aquaponics in a power outage?

Without pumps, dissolved oxygen falls (NMSU: low oxygen also stalls the biofilter). Oklahoma State Extension: “If electricity supply is unreliable, a backup power system should be installed”; its stopgap is pouring sump water into the fish tank every 1 to 2 hours until power returns.

What fish are used in home aquaponics?

Oklahoma State Extension calls tilapia “an ideal, hardy choice of fish for aquaponics”; its species table also lists bluegill, channel catfish and rainbow trout, with temperature ranges for each (rainbow trout optimal 14 to 16°C, about 57 to 61°F). Which species may be kept is governed by state fish and wildlife rules.

What food-safety rules apply to aquaponic produce?

The University of Hawai’i’s guidance (FST-38, 2009): rinse produce only in potable water, never system water; wash hands before harvesting; keep warm-blooded animals away and cull plants soiled with droppings; sanitize harvest tools and bins before each harvest.

Where to go next

Sources