Tank Oxygen Demand

Oxygen Requirement per Tank Volume

If there is one water-quality number that decides whether your fish live or die, it is dissolved oxygen (DO). Adult fish usually need > 4 mg/L. Juveniles and fingerlings are hungrier for it and want > 5 mg/L. What this calculator does is weigh the oxygen demand of the biomass against the tank volume through a simple mass balance. The term DO_target × volume_L gives you the standing pool of oxygen, and that consumption then gets compared against how fast aeration and surface diffusion put it back.

On the ornamental side, a 1,000 L aquarium will hold something like 10 kg of fish if you pair it with a decent air pump (Aero Tube, Tetra Whisper). Fish farms lean on paddlewheel aerators instead. Those churn the surface to pull air in and push out 1.5–2.5 kg O₂/hp·h. When a pond starts to crash you can buy time by dosing 35% hydrogen peroxide at 5–10 mg/L. To read DO itself, people use optical or polarographic probes (YSI Pro, Hach HQ-series).

Applications

People reach for this when sizing an air pump for a hobby tank, working out aerator power for a farm pond, or laying out a biofloc or RAS setup. It also answers the practical question of whether a given tank can move live fish safely. Hatcheries find it handy too, since calibrating oxygen during the fragile larval phase leaves little margin for guessing.

FAQ

What causes nightly oxygen crashes? In ponds, algae burn oxygen all night long since there is no photosynthesis to offset it. DO can bottom out in the hours before dawn, and that is exactly when most fish kills happen.

Does temperature matter? A lot. Warm water simply holds less dissolved oxygen. Saturation drops to 8.3 mg/L at 25°C against 11.3 mg/L at 10°C, which is why summer is the season to watch.

Is bottled oxygen worth it? Save it for hauling live fish or riding out a short emergency. If you are running a farm day in and day out, paddlewheel or diffuser aeration costs far less per kg of O₂ you actually deliver.