Herbie Overflow water level fluctuating

[hosfordryan]

I'm in the process of setting up my first saltwater tank. It's a 60 Gal cube with a custom 20G High as a sump. I'm finally at the stage of leak testing my plumbing. However, I can't get it to maintain a consistent water level in the overflow box.

I'm using a Herbie overflow and can't seem to match the drain rate to the return rate, thus causing the water level to fluctuate in the overflow box. Because of the small footprint inside of the stand and that I'm using a 20G High for a sump, in order to not have to reach far back to empty the skimmer/change out filter socks, I have it running front to back instead of (what seems like) the more common side-to-side configuration. From my research, it seems like having horizontal sections in your drain pipes is not ideal as it can make it hard to get a full siphon going for the main drain. Could that be why I'm seeing issues?

Here's my setup - Going left -> right is the return, emergency drain, and main drain.

I also only have about an inch between the top of the main drain bulkhead to the emergency drain, whereas I've seen something closer to 6" is ideal. Not much I can do about that with how the tank is drilled though (Tank is used and was already drilled).

Another question: I've heard that you must have your main drain outlet submerged in the sump in order to establish a full siphon. I don't have the space in the sump to set up an overflow into a filter sock, so in order to use a filter sock, I'd have to have the drain outlet stop above the filter sock (thus not submerged). Is there another way that I'm not thinking of to fix that problem? Or is it ok to have your main drain end above the water in the sump?

I appreciate any help.

 

[shwareefer]

Submerging the outlet is to reduce splashing not help with siphon. The inlet needs to be fully submerged for siphon. I assume your picture is with flow off. When things are correct and running, your inlet should be submerged with the water brimming and slightly trickling down your emergency drain. If the level is fluctuating in the overflow, you have intermittent siphon and need to close the valve more until the water level stays at the top of the emergency drain. You may need to remove the white insert in the emergency drain because it looks a little too high.

 

[shwareefer]

You can add a PVC elbow facing downward to the main drain to widen the distance between it and the emergency drain.

 

[WVNed]

If you don't have the main drain submerged air can enter from the bottom and travel up the pipe so it never fully purges.

 

[hosfordryan]

Submerging the outlet is to reduce splashing not help with siphon. The inlet needs to be fully submerged for siphon. I assume your picture is with flow off. When things are correct and running, your inlet should be submerged with the water brimming and slightly trickling down your emergency drain. If the level is fluctuating in the overflow, you have intermittent siphon and need to close the valve more until the water level stays at the top of the emergency drain. You may need to remove the white insert in the emergency drain because it looks a little too high.

Yeah, that picture of the overflow box is with the pump turned off. The emergency drain is about 3/4" below the top of the overflow box and about an inch and 3/4 below the rim of the tank. Is that too high? That's a good idea on the elbow for the main drain. I'll have to run to the hardware store to get another elbow and give that a shot

 

[hosfordryan]

If you don't have the main drain submerged air can enter from the bottom and travel up the pipe so it never fully purges.

If I have the main drain above the water in the sump, the flow looks pretty smooth and is practically silent while going into the filter sock. Would that indicate that there is a full siphon? Or could it still have some air trapped that is reducing flow?

 

[shwareefer]

Yeah, that picture of the overflow box is with the pump turned off. The emergency drain is about 3/4" below the top of the overflow box and about an inch and 3/4 below the rim of the tank. Is that too high? That's a good idea on the elbow for the main drain. I'll have to run to the hardware store to get another elbow and give that a shot

Normally you want the water to have 1/2" drop from the display tank level to the level in the overflow box. This again is for quietness. If the water is dropping 3/4" I'm sure that would be fine.

 

[WVNed]

If I have the main drain above the water in the sump, the flow looks pretty smooth and is practically silent while going into the filter sock. Would that indicate that there is a full siphon? Or could it still have some air trapped that is reducing flow?

I don't any way to tell that for sure. A drain runs faster without any air in it. It can enter from either end. If changing the top doesn't stabilize it I would friction fit an extension onto it and see if that does it and go from there.