When gardening, looking at things like soil moisture, soil tilth, or even looking at it under the microscope reveals insights about the medium of growth in which you have undertaken (soil). However in aquaculture, moisture and fertility issues are lessened yet the limiting factor of oxygen is ever-present. Oxygen is measured by parts per million in water and like pH the magic number is 7. When oxygen levels drop too low, fish slow down their eating habits which is not desired conditions especially when culture of fish is taking place. When oxygen levels
drop even lower fish kills are possible. Oxygen is not only ingested by fish but also bacteria which are the major decomposers of the system. Thus if too many nutrients are present from over fertilizing of the water, either from runoff of synthetic fertilizers or animals, bacteria proliferate when algal blooms take advantage of these abundant nutrient resources. The algae grow rapidly and abundantly but when their life expectancy of around 14 days happens chaos ensues as they die and then are consumed by bacteria. This is what happens every year at the mouth of almost every major river but is famous in the delta of the Mississippi River and its creation of the Gulf Dead zone. There a region the size of New jersey measured 13,080 square kilometers (= 5,052 square miles) has no life after the initial flush of agricultural nutrients because of the overload that comes from runoff from the vast corn and soy region. The algae and plankton thrive immediately from the excess nutrients but their overgrowth then leads to conditions with no oxygen as the bacteria consume and respire.
The Greenhouse of the Future ebook by Francis Gendron