I need to chime in here, been away since last post, Aquaponics 101 part 4 - system start up.

The older system where the DO measurements were made and reported with increasing DO did NOT have any water being jetted back into the tank. I have built systems like that, however. Regardless of theory and what someone else has written about aerators not providing DO I have the data to prove otherwise, as was given in my original post.

I included water jet back in the "system design" portion of Aquaponics 101; for I have information from others that tell me this is a good way to inject DO into the fish tank water, but again, it was not implemented in the system where I made and reported the DO measurements above.

In the systems I built where the water jet back was part of the system, I measured a DO of over 8.0 ppm. But, there were no fish in that system at the time of measurement; for I was testing a new design and trying to determine how to increase the DO in the water. I still have more testing to do on that system by turning off certain sources of aeration and then testing the DO. Unfortunately, due to some building construction, I had to dismantle the test system before completing all of the DO measurements. I will be resuming those measurements soon and then I will hopefully have a better idea of what elements add DO to the water and how much.

To measure is to know.