Biology & ecology
Dissolved oxygen
Also known as: DO
Dissolved oxygen (DO) is the concentration of oxygen dissolved in the water column, measured in milligrams per liter (mg/L). Healthy Florida ponds run 5–10 mg/L during the day. Photosynthesis produces oxygen during daylight; respiration consumes it day and night. DO drops to its daily minimum just before sunrise. Below 4 mg/L, most game fish stress; below 2 mg/L, fish suffocate. Decaying vegetation adds bacterial oxygen demand at night, which is why post-treatment fish kills are predictable. Aeration is the single highest-ROI investment for a stocked pond.