When I was in High School my Science Club was in charge of monitoring a local freshwater stream. When we did our monthly water tests on the stream we always measured the Dissolved Oxygen levels and reported that to our State Department of Wildlife Conservation. However, in the aquarium hobby I haven't seen many people talking about DO levels in their tanks. Do you guys bother testing for it? If so, what levels are you looking for and what test do you use. If not, why not? Is this parameter not important? Just trying to learn more about reefing