Can someone explain whats happening here?

[Magzire]

Any ideas how this is meant to work?

 

[Tula]

I have no idea, maybe @MitchM can help out

 

[Magzire]

I have no idea, maybe @MitchM can help out

Actually I think the loop is there so bacteria can abort oxygen with a slow flow rate which then supports anaerobic bacteria for denitrification. I doubt this works at all.

 

[MitchM]

I wouldn't draw any conclusions from that video.
I think what is most likely happening is that the nitrate testing bottles were not shaken enough for the second test.
We don't know anything about his feeding regime, algae levels, filtration, water changes, etc.