Replace the ball valve with a gate. If you are seeing that much fluctuation I am assuming that it is due to the rising and falling level in the overflow caused by the inaccurate adjustment of the ball valve. Either that or you are having some serious evaporation happening. Gate valves are minutely adjustable and allow for the fine tuning required to maintain the proper water level in the overflow.

Doug.

The gate valve placement doesnt matter. The gate is used to limit the flow out of the display to the point that the water level inside the overflow box is high enough not to make any noise falling but low enough not to go down the emergency drain.

Yeah...therein lies my mistake...I didn't figure out the height thing properly...now the plumbing is "permanent" at least until I decide to empty the tank to fix it. I don't get much noise...less than my regular overflow...but still not completely silent because of my calculation error.

OK, so my problem is the ball-valve - I'll change it to a gate valve. Do they make 1.5" gate valves?
The fluctuation in my sump happens because the ball valve is either closed too much or open too much, and the pump either pumps out faster than it gets to the sump, or the sump fills faster than it can pump out.

Yes, they make 1.5" gate valves. They aren't too difficult to find.

Your explanation for the sump water level doesn't make sense, though. Is the water from the tank falling into an overflow box? Basically, the amount water that you pump INTO the display tank ALWAYS equals the amount that falls out. It just does.

If you are pumping 400gph into the display tank...and only getting 300gph back into the sump...your display tank would be overflowing!

The key to a Herbie is the fact that a given pipe size will actually handle a variable maximum amount dependent on the water pressure behind it. So if you dial back your Herbie valve, the water in your overflow box should start to rise....but it won't rise forever...as the water behind the valve rises, more pressure is exerted which forces more water down the pipe. This hits equilibrium and the water height behind the valve stays constant.

Could you post pics of you overflow and plumbing? Sorry mseepman if we are taking over your thread, but this will be a good read for peeps wanting to do a herbie style overflow. Properly set up a herbie should be silent and fail safe.

Doug.

No worries...I thought I was so smart doing a herbie...yet I still made mistakes that have made it less than a "true" herbie.

I believe the problem was with the fact that I didn't have a stand pipe on the Herbie. I stuck one in the drain and it's been steady since.

You really should post a photo of what you've got there... It is necessary to have a standpipe on the emergency overflow drain, but not in the drain that actually gets used. (the one with the valve on it).

I'm curious to see what you've done there.

Herbie overflows
 

I have a 90 gallon with dual corner overflows. One is a 2" the other is a 1.5", can use those in a Herbie style setup? Maybe if I used the 1.5" for the main adjustable drain and the other side for the emergecy overflow. The thing I cant see working would be that both sides would have water overflowing through the skimmer holes.
Also, how would I incorperate a sock filter in the sump?

Gerry