What level in mg/L?
Keep it above 5 mg/L for most warm-water species and above 6–7 mg/L for cold-water species like trout and salmon. Below 3 mg/L can be lethal for many species.
Free toolWater Quality CheckerWhy does oxygen drop?
- High water temperature: warm water holds less oxygen.
- High biomass and increased consumption after feeding.
- Photosynthesis stops at night: the lowest values appear towards dawn.
- Days when currents weaken or the water stratifies.
When should it be measured?
The most critical reading is taken just before sunrise. In warm periods measure at least twice a day, ideally continuously with a sensor.
What to do when oxygen falls
- Reduce or stop feeding immediately.
- Increase aeration or oxygen supplementation.
- Postpone stressful operations such as grading or net changes.
FCRSOFT
FCRSOFT does this for you automatically
You don’t need to do the calculations and checks on this page by hand every day. FCRSOFT derives them all automatically from the records entered in the field.
- Oxygen, temperature and pH readings are recorded per cage.
- Sensor data is collected automatically, with instant alerts when thresholds are crossed.
- Water quality history is reviewed side by side with FCR and mortality data.
Last updated: 10/3/2026
