Here are a couple threads that talk about lift rates and as far as I know...Vertex is the only company that has done the testing to be able to produce their lift rates...
https://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=280961https://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=490146You'll want to start by estimating the gallons in you pond. There are many "Pond Volume Calculators" on the web that will help with that. You may have to just use some basic dimensions and give your best guess at average dimensions, but it will be good enough so long as you oversize your system to do the job all at night.
Using the following sites...
https://www.pondvolumecalculator.com/https://vertexaquaticsolutions.com/pond-and-lake-aeration-calculators/and using 50 foot average width, 226 foot length, & 12 foot average depth yields just over a million gallons and a 1/4 acre surface. Unless your pond is strip-mine-like with very steep sides...I suspect the average depth to be much less than 12 feet. Play with the numbers as you see fit and start calculating turnover rates. I would used Vertex lift rates if going with a different brand of membrane diffuser that did not have that info available. Keeping in mind that there could be some sizable differences between the two designs. Whatever you end up with, you can test the turnover rate by watching the water column temperatures at the bottom compared to the top. Approximately one turnover happens when the temps at the bottom and the top are within a few degrees (2-5) of each other. At least that's my theory. Start the system up gradually as prescribed (not all ant once)...once you get to the point of running about half the day, you will see that the water temps are pretty much the same from top to bottom when the aeration turns off (given the system size is adequate). Let 12 hours go by with it off and you will see a temperature difference again between top water and bottom. Start it up and check the temps every hour (in the middle of the pond). Once you see very little difference in top and bottom temp...you have your turnover rate (or very close). I consider top water temps to be at about 18" down and bottom temps to be at the very bottom (within a few inches at least). The top 6" of water can always be hotter in the summer even with air on due to the effects of the sun and ambient air...that's why I only look at the 18" mark for this test.
EDIT: At a very quick glance... a 1/4 hp pump (piston or rotary vane) and 2 diffusers would be a safe bet. You need to know what the output (CFM's) of the pump would be a the depths you'll have the heads and make sure you are not over-driving the heads. You may find that you need to add a head to lessen the flow to the original 2, or use a smaller pump. This all depends on what heads you go with and how much CFM they suggest pushing through them.
