Fluctuating water level in herbie overflow compartment

[DjPhato]

Hi all, since I started the tank I noticed that the water level in the overflow compartment is fluctuating a lot. I have an herbie overflow and attach a picture here with a sicce syncra 6.0 as dc pump return.
I started with the return drain valve at certain position and pump at 16% but I needed to open a bit more the return valve many times. Basically every few days I notice that the level of the water in the overflow is rising and I open the valve a tiny bit to readjust the level. Why is this happening? I was expecting to find an equilibrium…tank is running since few weeks now. First time using herbie, any suggestions?
Main drain is the one with the valve, emergency is the one without valve.
Thanks

 

[JohnK]

Herbies tend to get close, but retain some slight fluctuation, often enough to drive a reasonable person slightly mad.

I find that if you are closer to the high end of the potential flow rate they are (might be) a little easier to keep dialed. (ie turn up the pump, open the drain valve to accommodate the flow - then see if it becomes any more stable at that higher flow).

Otherwise, I hate having to fiddle thing things all the time so I settled on this modification to my herbie emergency drain standpipe. It's not keeping the emergency entirely dry as the herbie design recommends, but hasn't caused any problems over the 10 plus years I've been using this. (adding picture in a minute)

 

[JohnK]

1/2" down elbow and short pipe. It is also restricted about %50 inside so it can only accommodate a bit more than a trickle. Gate valve on main drain adjusted so the water level sits at the bottom to middle of the 1/2" down elbow. Emergency drain stays silent, only a slight trickle going into it at most, acts like a Bean keeping itself adjusted. This way I end up fiddling with the gate valve once in a few months.