Can’t keep overflow box balanced

[Cruzersmith]

Just looking for ideas as to why my old cpr overflow box keeps losing the full siphon in the exterior compartment in the middle of the night and making so much noise it wakes me up so I have to get up and close the gate valve enough to quiet it down. Then by morning it is into the emergency overflow so I have to open the gate valve enough to get it back into balance until the middle of the night again. I have a redsea 250 mat in the sump and I can’t see why it should but am wondering if the way it fills itself until it hits the sensor and then empties some after a mat rotation would effect anything? Otherwise I just don’t get it. I’m running a 400gph pump but don’t know the cpr specs anymore as it’s ancient. Funny thing is I tested this setup without the roller mat for 2 solid weeks on a test tank with no issues at all.

 

[wvned]

Does the water level in area the drains empty into go up and down depending on the condition of the mat? The flow in a full siphon drain changes as the head height does.
If the water goes down in the sump it speeds up.
I would try to adjust the drain when the mat is clean. Then as it dirties more water will go down the emergency until the mat advances then it should return to the previous flow.
It doesnt matter if a little goes down the emergency drain.

 

[Cruzersmith]

Thanks, yes the sump level does change. I didn't think it was enough to change things so much, but I will go with your recommendation. Thanks again.