Expert: Henry Boyter - 5/6/2002

Question
Hello Henry;
Suppose we have 2 water samples; how can we compare the oxygen concentration of these samples with each other by a simple methode. If there is a way, I could assess the oxygen content of my aquarium in comparison with tap water.
                Thanks;  Soheil

Answer
There is no simple method in the two kinds of DO tests.  The easiest is of course the membrane electrode and meter.  But very expensive for an aquarium owner.  The others are titrations which require special chemicals and have many inteferences, so any chemicals added may screw things up.  There is no simple method that works in general cases.  Under normal aeration conditions, the water in an aquarium will be saturated for that temperature and pressure.  Only if you cheat on the air or have rampant algae will there be a problem.  Remember, you can't add two much air, the excess bubbles off.  In tap water, it depends on several factors.  Well or pipe?  How long in the system?  First fraw or 5-minute draw?  Tap water with just a couple of minutes of aeration will also be saturated, but it is most likely close to begin with.