QA - thanks, I also have enjoyed the conversation. When I was researching canned systems, they were either fairly small at 5 - 6 psi discharge or pretty big as you mentioned. I thought about building my own system using the septic pumps but my pond fluctuates in depth 3' - 4' at times and I just got nervous precisely due to not having a good comfort level with the line loss - I also might have gotten a bit lazy. I was also afraid of condensation dropping out in the line and adding to the line loss over time. I believe we are both engineers so a lot of this comes somewhat intuitively. A lot of folks on here that ask for help seem to be looking for rules of thumb type guidance. It was good to have the conversation in technical detail because it helped me arrive at a rule of thumb.

That being: If your system is going to be fairly simple, 200' - 300' of line with a couple of diffusers, use a 0.5 psi/ft gradient for sizing the discharge pressure and you are probably going to be OK. If you think you are still on the edge go to 3/4" line. The deeper the pond the bigger the safety factor that results from using a 0.5 psi/ft gradient.

Hopefully that will help anyone who is interested but zoned out when things got deep. Regards.........................