Inputs · Water
Aeration and dissolved oxygen
Dissolved oxygen is the water quality factor that kills fastest: fish can die within hours, sometimes minutes, when it runs out. Fish, plant roots and the biofilter bacteria all draw on it, and warm water holds less of it, which makes Florida summers the risky season. Run air pumps all the time, add more in hot weather, and have a backup for power cuts.1, 2, 4
Why you need it1, 2, 4, 5, 3
FAO calls oxygen the parameter with the most immediate and drastic effect in aquaponics and puts the optimum for fish, plants and bacteria at 5 to 8 mg/L; tilapia and carp can survive 2 to 3 mg/L, but it is much safer to stay higher. SRAC 452 says keep it above 5 ppm (and above 60 percent of saturation) for warm-water fish, and that nitrifying bacteria work poorly below 2 ppm. UF/IFAS FA27 recommends 5 mg/L or more, says most species are distressed at 2 to 4 mg/L and usually die below 2 mg/L. The UF/IFAS guide HS1252 names low oxygen (below 3 ppm) with high ammonia as the most common causes of fish deaths. Plants suffer too: SRAC 454 says low oxygen at the roots cuts water and nutrient uptake and, with the high carbon dioxide that goes with it, encourages root disease. Signs: fish gathering at the surface gulping air (piping), crowding around air stones, or suddenly not feeding (FAO, FA27, SRAC 452).
How to use it1, 3, 5, 2, 4
Keep water moving and add air: FAO's two tools for small units are water pumps that keep water flowing and air pumps feeding air stones in the tanks; deep water culture and NFT units especially need the extra air. Use good air stones, since smaller bubbles release oxygen better (FAO). SRAC 454's commercial raft system holds about 80 percent saturation (6 to 7 mg/L) with an air diffuser every 4 feet along the raft tanks. Increase aeration in hot places and hot seasons (FAO). Shade: FAO and HS1252 say to cover fish tanks against sun and algae; HS1252 suggests about 30 percent shade over plants in hot summer months. Back up the power: FAO calls battery backups for air pumps a valuable asset that have saved countless fish, and recommends a DC backup where power is unreliable; failing that, bail water from the sump into the fish tank every 1 to 2 hours until power returns. SRAC 452 calls backup power essential, with an automatic transfer switch to start a generator and a phone alarm. Measure: FA27 names electronic oxygen meters as the most efficient tool and chemical kits as accurate but slower; FAO says small units can instead watch fish behaviour closely and keep pumps running constantly.
In Florida4, 2, 3
UF/IFAS FA27 says oxygen depletions are most likely to kill fish in hot summer weather: warm water holds much less oxygen (at saturation, 7.4 mg/L at 90 °F against 11.9 mg/L at 45 °F), fish need more oxygen as they warm up, and muggy, overcast, still days and summer thunderstorms often set off depletions (its examples are ponds, where algae and plants make much of the oxygen). SRAC 452's table gives saturation of 7.53 mg/L at 30 °C (86 °F) and 7.13 mg/L at 34 °C (93.2 °F). SRAC 452 also shows how little time a power failure leaves at Florida-like temperatures: in a warm-water system at 84 °F holding a quarter pound of fish per gallon, oxygen falls from saturation to a stressful 3 ppm in 16 minutes, and in under 6 minutes at a pound per gallon. SRAC 454 adds that tropical outdoor systems benefit from fully shading the fish and filter tanks, and that floating rafts keep water a few degrees cooler than open water.
Cautions1, 2, 6
Algae compete for oxygen at night and can crash it before dawn; FAO says to shade all water surfaces to prevent algae. Carbon dioxide builds up alongside low oxygen: SRAC 452 says fish are stressed above 20 ppm and that aeration removes it. In an intensively stocked recirculating system, aeration failure can lose the whole crop in half an hour or less (SRAC 451). Pressurised aeration that draws in air can supersaturate the water with nitrogen gas, which harms fish (SRAC 451).
What to buy1, 4, 2
An air pump sized for your tanks with fine-bubble air stones (FAO), a battery or DC backup for the air pump (FAO), and a way to measure oxygen: an electronic meter or a chemical test kit (FA27). SRAC 452 adds an alarm for power failures at larger scale. No source names brands.
What this page doesn't cover yet
- FA27 is written for ponds, where algae supply much of the oxygen; its summer and storm warnings are used here as Florida context, not as tank-system rules. Its advice to run pond aerators only at night does not apply to tank systems and is left out.
- No source gives air-pump sizing (litres per minute per tank volume) for home systems.
- No source covers hurricane or multi-day outage planning in Florida.
- FA27's distress range appears as '24 mg/L' in the extracted text (a dash lost); read as 2 to 4 mg/L, which matches its summary.
Sources
- Small-scale aquaponic food production: Integrated fish and plant farming (Somerville et al. 2014). Food and Agriculture Organization of the United Nations (FAO), FAO Fisheries and Aquaculture Technical Paper 589. Read 2026-11-02.
- Recirculating Aquaculture Tank Production Systems: Management of Recirculating Systems. Southern Regional Aquaculture Center (SRAC), SRAC 452. Read 2026-11-02.
- Recirculating Aquaculture Tank Production Systems: Aquaponics—Integrating Fish and Plant Culture. Southern Regional Aquaculture Center (SRAC), SRAC 454. Read 2026-11-02.
- Dissolved Oxygen for Fish Production (Francis-Floyd). UF/IFAS Extension, EDIS, FA27. Read 2026-11-02.
- A Practical Guide for Aquaponics as an Alternative Enterprise (Tyson and Simonne 2014), archival copy. UF/IFAS Extension, EDIS, HS1252. Read 2026-11-02.
- Recirculating Aquaculture Tank Production Systems: An Overview of Critical Considerations. Southern Regional Aquaculture Center (SRAC), SRAC 451. Read 2026-11-02.
Restated in our own words from these documents, written 2026-11-02. Doses are the sources' figures; test your water before and after.