Imagine standing neat a tank, with the kit. You take some water, and add it carefully into the measuring tube to the required level.
That is, you poor water, thought to contain little oxygen, through air which is 20 % orxygen. What happens? Oxygen will dissolve into the water
If you then measure 5, you will only know the real value will not be more then 5. And most likely, without any certainty, that it is more than the last time, when the kit said 4.
Sorry: Brian Greene is a professional. I can't see a waste of anything. The moving is in order to dissolve the chemical indikator.
Of course: electronic measering is better but expensive.
For our hobby a test kit by JBL or else will do. Recomended is the reading of the user manual. In particular the "overflowing" of the cuvette is essential. This way you won't add oxygen of the natural environment.
Only problem for all test kits: it is difficult to find the right value, the "shades" of blue are sometimes irritating.
I did a last test series about 6 years ago, just to know. Controlled by a professionel electronic measering unit. Variations were small and mostly due to the "colouring" interpretation.
I agree that there can hardly be a lack of free oxygen in a tank with the right loach set-up. Means: no overstaff, not to high temperature, not over-planted (oxygen consumption at night), not overfed (permanent oxygen consumption); with strong water movement at the surface.
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