Unlike the other tests where I collected all the water for the various depths, then did all the tests together, I had to draw the water and do each test immediately. The water is put into a test tube with a very small surface area and agitation of the water is kept to a bare minimum, so it appears that the amount of oxygen that could dissolve into the sample during the test was minimal. After the test was done, I left the sample in the test tube and watched the color change gradually as the dissolved oxygen came up. It took several minutes.