Thanks for the testing. I am a newbie and found airlift is an interesting subject and been reading those posts in Koiphen. I have some thought on your test set up and latest idea from Luke...
Based on what I have read, with certain air pump and pipe diameter, there will be a certain depth that gives you the most flow. In this test, The “most flow” will results in the MOST amount of water overflow (water lost). With your current set up, the pipe MAY NOT be long enough to find that “sweet” depth? That’s why your first and second tests gave you the same water level on the clear tube (1st test with the air stone at the bottom, 2nd test with air stone drop slowly)?
If you make the tube longer, as you slowly drop down the air stone (deeper than your current pipe allows), the water may overflow more. If that occurs, the water level on the clear tube will be lower (make sure you re-mark it when you use a longer tube so that you have the same distance from the top to the mark). At some point, the water will stop overflow, that is the “sweet” deep that you look for.
Now, hopefully your pipe is long enough.. To confirm the “sweet” deep, you do the next test
You know the deep of the “sweet” spot on the previous test, let say it’s X ft.
1) Refill water in the pipe
2) Lower the air stone more, let say 5 or 8 inches deeper than the “sweet” deep, X ft in the previous test. (The expectation here is that because air stone is deeper, the back pressure is higher and results in less efficiency, and the water on the clear tube will be higher.. Or in other word, the total water overflow is less)
3) Turn on the air pump.. I think if you can kink the air tube and release the air slowly to avoid the turbulence, that may give us a more accurate result..
4) Observe the results to see where the water level in the clear tube is.. If it’s higher, which mean we lost less water, which mean less “flow”..
I think this is what Luke mean in his latest suggestion.. One think that he may not have thought of was the tube was NOT long enough….
Well, hopefully I make some sense here...