What is dissolved oxygen (DO) anyway?
Every living thing takes up oxygen. Oxygen in water is critical for critters to survive. Dissolved oxygen in water can be measured in parts per million (ppm). The air we breathe can also be measured in the same units, although the scale is much different. Imagine the room filled with one million white marbles. The air we breathe is composed of about 21% oxygen… which can be measured as 210,000 ppm. Translated to our imagination, that means over 200,000 out of every million marbles would be blue… representing oxygen. We breathe well with 200,000 blue marbles. Fish, and many other aquatic critters, live in their watery world with the oxygen dissolved in water measured between 5 and 20 ppm. Translated, fish only need 5 blue marbles out of every million marbles to survive. This is one good explanation for why we don’t breathe well under water. Below 5 ppm fish and many other aquatic animals begin to stress, and below 3 ppm many can’t survive. What‘s the deal about dissolved oxygen (DO) in
