QK - I would not buy a DO meter for your situation or what you need done. Look into having someone come in and do some measurements if you absolutely need to know the DO near the bottom. Maybe Aqua Doc or a fish farm near you? Here is a cheaper alternative to a DO meter. Get an electronic temperature meter; a lot cheaper than a DO meter. Measure the temperature of the water at the surface and near the bottom. If the temperature is within 3F-4F (maybe5F) of the surface and the bottom, then the bottom usually has enough DO for aerobic bacterial growth. My theory: As the circulation stops the water near the bottom begins to cool. Under many conditions as the bottom water cools the DO also begins to get consumed - gets lower. As the bottom water at 2" above the sediment approaches 5F difference of the surface temp the DO drop ed to below 1-3ppm.
Electronic thermometer example:
http://www.amazon.com/Portable-Finder-Sensor-display-back-lighting/dp/B003OUQ1B0/ref=pd_sim_sbs_e_2There are a numerous exceptions to this rule depending on pond conditions, but it applies to many ponds such as yours. One of the exceptions is how well and how long the pond was circulated prior to stopping the circulation. Some other exceptions are how clear the water is and what suspended solids are in the water column. Those with DO meters can test this theory and report their results here or in a new thread. The accumulative results will be beneficial to all of those that aerate their pond.
