Herbie overflow.......out of patience

[Reef Tank 2.0]

I am out of paitence. I don't know what else to do. I have spent the last two hours trying to adjust my gate valves so that the overflow drain level STOPS fluctuating. I haven't changed anything, other than adjust the gate valve a 16th of an inch at a time.

I have opened my return gate valve all the way. From that point, I adjust the drain valve to the point that it is A) quiet, and B) stable. A) isn't a problem at all. I can quiet that down pretty quick.
B), right when I think the level is finally stable, I watch it for 5-10 minutes, and I watch it slowly creep upwards or downwards. The further down it goes, the louder the overflow becomes.

I don't understand why this is happening. Nothing is changing from the sump, up to the overflow.

I have the system filled with water, rock, and sand, and getting ready to drop in raw shrimp tomorrow to begin the cycle process.

I understand one needs patience in this hobby, but this is ridiculous. A 16th of an inch should not change the level by INCHES!

i can only assume you don't want any water draining through the emergency line. which is what i am trying to avoid. but on the flip side, if i do let the water flow through the emergency line AND the main drain line....does this cause an issue? when it does flow through both, things seem to stable out and become a lot quieter.

i sat here and watched this water level drop 2" with me not changing a thing. then it creeps back up, very slowly.
when i go to the sump, everything is quiet and there is no gurgling or anything coming from these pipes. i don't know what the issue is up here at the tank. why is this water level fluctuating?

a gyre wouldn't cause this would it? i do have that in place

I am at a loss, can anyone help?

Here is an image of the set up instructions I used..

[Wall_Tank]

Adjust it so the water level rises to the emergency stand pipe.  There should be a very small trickle down the emergency pipe?.  But it should not make noise.

[JSellars]

Definitely okay with having it trickle down the standpipe. Also, is this a completely all new setup? Do you have a DC or AC return pump?


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[Reef Tank 2.0]

once i adjusted the flow to trickle down that emergency pipe, things became more stable and quiet.  that made a world of difference.   thank you!