YSI optical DO meters are supposed to be very accurate, thus the meter is likely okay. If you have the meter measure the surface oxygen in another local water body that is 'normal' and high near 8-10ppm. Or - if meter is at the cabin then when you return check DO in another very clear pond/lake to verify meter is reading a high DO.

Heavy cloud cover and storms on the previous day of the DO check probably reflects low DO production from the previous cloudy day and night.

Emerald green water with a dense algae amount in the pond could be having an influence on the DO due to more or lots of respiration and less photosynthesis. Next time there, check the surface DO at mid afternoon on a sunny day and the test it in the early morning just after sunrise when DO should be low compared to mid day; compare the two readings. This should give a rough estimate of the DO increase due to photosynthesis. Aerators appear to be mixing well the water column top to bottom. Aerators could be mixing low DO deep water throughout the pond during the day keeping DO at all depths lower. Amount of DO production due to photosynthesis will depend on the algae density (numbers per ml). Light penetration will not be very deep in emerald green water causing more respiration deep compared to DO production in the surface shallow layer from photosynthesis. Do you have a homemade secchi disk to get a clarity measurement? Secchi disk can be a rough estimate of algae density for comparison purposes.

Last edited by Bill Cody; 10/02/18 10:59 AM.

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