At my property, I have for some time now experimented with EM. I have also found that 'feeding' EM form time to time with sugar and fertilizers (like ammonium sulphate) help. First, I fed them weekly. Then I found that they depend on environmental factors like temperature, sunlight and rains (like other plants), so I am learning to feed them 'as they need'.

What is the 'right' (optimum) population of EM in an environment for the purpose of cleaning water?

I don't know. I am working with just senses observation. When the water is clear, not smelly, with little fish swimming in, and grasses around there look healthy, then I accept the water quality. Otherwise, I add more 'feed' or more 'EM'.

Obviously, this is hardly, a modern scientific experiment. But the main thing is "I am testing a simple theory" that the health of people (and other lives) in an environment depends on the health of micro-organisms (primary workers) in that environment.

"Feeding" (and not-feeding) may be one important factor in managing environment.