Frank, You may want to have a BOD test but be aware that it can and does change. The demand varies with temperature, sunlight time of year etc. Results are normally expressed in Mg/L or ppm and the goal number would be "zero"or in other words the supply of O2 meets or exceeds the "demand" You may see a number like 10-12 or even 15 on a test report. You may also find a negative redox or "ORP" (Oxidation Reduction Potential) with the test results of a redox test. They also can swing as most waste water treatment plants will do a constant monitoring of their redox value for this reason.When o2 is added to the water obviously the intended result is to lower the BOD number and meet the demand and when this occurs the ORP may rise to a positive millivolt reading which is a good.A lot of the tests are sensitive to timing as is DO. Test for DO in the early AM and it will be lower than the early afternoon on a sunny day.Test in the top 24 inches and will be higher than on the bottom. Point being on test results be aware that they are but a "snapshot" of the immediate present and not always the longterm average. Even a composite sample can mislead.Ponds with high amounts of organic sediments may have a negative redox and a high "demand" BOD. Hope this helps. Ted