Think B.I.G. Hawaiʻi← All toolsSize a backyard fish-and-greens system for 1 to 12 people. Every number comes from University of Hawaiʻi CTAHR designs tested in Hawaiʻi, with the source linked beside it. The parts list links to places to buy, starting with East Hawaiʻi.
A step-by-step build plan for the options you’ve chosen: site plan, phases with checklists, parts and where to buy, budget, routine and sources.
Top view, drawn to scale from UH's bed layout. Tank footprints are approximate.
Quantities follow the UH unit design: one fish tank paired with one 4×8 ft bed. Ask local stores first; mainland vendors may not ship to Hawaiʻi.
UH researchers Harry Ako and Adam Baker built a low-cost system at Mānoa from one simple unit: a stock-tank of tilapia feeding one 4×8 ft lettuce bed S1. The planner counts how many of those units your household needs, then adds them up. Keeping each unit at UH's tested ratio is what makes the numbers trustworthy.
| One UH unit | Value | Source |
|---|---|---|
| Fish tank | 85-gal stock trough filled to 52 gal, shaded with a tarp to stop algae | S1 |
| Fish kept in the tank | About 5.5 lb of tilapia (roughly 60 three-inch fish), after the biofilter is established | S1 |
| Feed | About 6.5 tablespoons (1.5 oz) a day of 42% protein trout feed, split into two meals | S1 S2 |
| Biofilter | 2.6-gal submerged cylinder of PVC media | S1 |
| Aeration | One 50 W air pump serves at least three tanks (CTSA #161 uses 25 W for a slightly larger tank) | S1 S2 |
| Grow bed | 4×8 ft plywood box, 2×4 walls, double 6-mil liner, 48 plants, 48 heads every 5 to 6 weeks | S1 |
| Moving nutrients | 5 gal of fish water into each bed daily; top the fish tank back up with clean water | S1 |
| Fish growth | Fish grow about 50% in 10 weeks, so thin and harvest about that often | S1 |
| Feed conversion | 1.1 lb of feed per lb of fish on a 45% protein feed in a CTAHR aquaponics trial (0.8 on a 35% feed, with slower growth). Working tilapia farms see 1.4 to 2.0, so the planner’s better case uses 1.5. | S3 S32 |
Fish yield is given as a range. Ako's observed growth (50% in 10 weeks on 5.5 lb of fish) works out to about 14 lb of whole fish per unit per year. Running the same 1.5 oz/day of feed through a typical farm conversion ratio of 1.5 lb of feed per lb of fish gives about 22 lb S32. (CTAHR’s feed trial did better, at 1.1 S3, but working farms rarely match trial conditions.) The conservative setting plans on the lower figure. Real results depend on fingerling quality, water temperature and how consistently you feed.
Water temperature matters. Tilapia grow best at 81–86 °F (27–30 °C) S28, and a trial found markedly slower weight gain at 64–72 °F than at 79–86 °F S33. Friendly Aquaponics in Honokaʻa saw lettuce harvests nearly halve, and fish growth slow, in a cooler summer S23. Expect slower results at upland sites.
Feeding rate. UH feeds about 1.5 oz a day per 4×8 bed, roughly 14 g per square metre. That is deliberately low: the FAO small-scale manual recommends 40–50 g per square metre a day for leafy greens S28, and the University of the Virgin Islands 60–100 g for raft beds S29. UH makes up the difference with potassium and iron. Choose “Standard FAO/UVI” to put about three times as many fish on each bed (about 4.7 oz of feed a day); that needs a pump to circulate water through the beds, as in Friendly Aquaponics’ low-density systems S30.
One big tank or one per bed. UH tested one small tank per bed. The planner can merge them into a single tank holding the same total water, the same weight of fish per gallon and the same total feed, so the chemistry each bed sees doesn't change. Ako titled his guide for "small-to-large" systems S2, and Hawaiʻi growers run big tanks. One Big Island family stocked a 1,500-gal tank with 800 tilapia S23, and a current CTAHR-advised project uses 1,000-gal catfish tanks S21. The trade-off: one tank is one point of failure. A leak or a bad night can take every fish at once.
Running without electricity. In UH's design the only electrical part was the air pump, which gave the fish oxygen and prevented denitrification S1. The no-electricity mode drops it three ways:
UH has not published growth results for catfish aquaponics or for tilapia without aeration. In those cases the planner reuses UH’s aerated-tilapia feed and yield figures and marks them in yellow. Expect to adjust once real results come in.
Fish usually set the size. One unit makes far more greens than fish. A household that wants fish for dinner regularly needs more tanks than its salad needs beds. Instead of building extra beds, the planner can send each extra tank's 5 gal/day of nutrient water to fruit trees or a garden. Hawaiʻi Sea Grant describes a farm doing exactly this, irrigating a quarter-acre avocado and citrus orchard with tilapia water S11. That step goes beyond Ako's published design, so the planner labels it.
Lettuce sits in 2-inch net pots pushed through a floating polystyrene panel. Water stands 2.5 inches deep, just reaching the bottom of the pots, which leaves a 1-inch air gap under the panel S1. Roots hang through that moist air and down into the fish water. Ako compares the gap to well-aerated tilled soil S2.
UH-made videos. Each opens on YouTube or the UH site.
| Measure | Target | What to do | Source |
|---|---|---|---|
| Ammonia | < 1 ppm | Feed less until it falls | S1 |
| Nitrite | ≈ 0.3 ppm | Biofilter still cycling; hold stocking | S1 |
| Nitrate | ≈ 47 ppm | The working target for good plant growth | S1 S2 |
| pH | ≈ 7, never below 6.0 | Add potassium hydroxide flakes daily at 1/10 of feed weight (or potassium carbonate) | S1 S2 |
| Dissolved oxygen | > 5 ppm in tanks | Check air pump and stones | S2 |
| Iron | Fish water runs short | 1/8 tsp iron chelate per bed, weekly | S1 |
| Uneaten feed | 5–10% left after 10 min | More left over, cut the meal; less, raise it | S1 S2 |
Rain catchment water is soft and barely buffered, so pH drifts down faster than in UH's tap-water trials. Test pH every day for the first month. CTAHR advises potable water and, with catchment, following catchment-hygiene guidelines S5.
Imported pellets are the one input this system can't make for itself yet. These steps cut that dependence and keep nutrients on your ʻāina. CTAHR's work on these is early-stage, so keep commercial feed as the base.
The semi-slug that carries heavy parasite loads is established from Volcano to Kalapana, through Hilo and into North Kohala S8. A 2023 UH study found stressed snails can release infective larvae into their slime, though the larvae die once the slime dries S7. CTAHR's farm practices S6:
Nile tilapia have overwhelmed the Wailoa River and Waiākea stream and pond in Hilo S14. Put screens on every overflow, site tanks above flood level, and never release fish.
Restricted-list species need a state permit to import and to possess S13. Buy fingerlings from a Hawaiʻi hatchery and ask the Department of Agriculture and Biosecurity's Aquaculture & Livestock Support Services (808-483-7130) which species and permits apply to you S15. Sea Grant's permits guidebook covers the rest S18.
Keep birds, dogs, cats and rats away from tanks and beds, use netting, keep harvest tools and bins clean, and use potable water S5. Selling any produce or fish brings legal food-safety duties; read CTAHR's FST-38 first S5.
Potassium hydroxide flakes are caustic: wear gloves and eye protection and store them dry, away from children. Standing water in rafts can breed mosquitoes. UH notes some growers keep guppies or other small larvae-eating fish in the beds S1.