Shaft Problem

[Joko]

Hello marine friends
I have a problem with my overflow shaft, and unfortunately I don't know what to do next. My water level in the overflow shaft remains constant for a few days, and then the water level in the overflow shaft drops a few cm, although I have not changed anything, which is annoying because mine is rising Water level in the technical basin, and then changes the way my skimmer works. Would be happy if someone of you could help me in any way. Thank you very much

 

[blaxsun]

I would try closing the gate valve just a bit and monitor. I have my water level in the overflow set to just at the rim of the emergency overflow.