Drain line bubbles/noise

[hoffmeyerz]

Still pretty new so I'm looking for suggestions. Running a 75 gal tank with a Lifereef overflow box and sump system. Tank's been running almost six months and doing well but the drain line causes a lot of bubbles as it empties into the sump. Every now and then you can hear a stretch of large bubbles. The biggest problem I'm having is the bubbling creates enough salt creep that my salinity has a habit of dropping. I started with a 1" drain line then changed to 3/4". That and the silencer in the overflow with some air tubing down the drain helps quite a bit but I'm finding I need to keep adjusting the air tubing almost every day.
Is this normal upkeep or is there any other tricks like maybe using a drawstring filter sock or putting a valve on that line?

 

[lapin]

From what I see online the overflow has only 1 down tube. Is this correct?

 

[Sean Clark]

You need to put a restriction on the drain or pump with a valve to balance the system. That should eliminate the bubbles and noise.

And Go Blue!

 

[hoffmeyerz]

Yes there is only one drain tube in the overflow.
I also have a ball valve on the return pump that I adjusted where things seemed to balance. Right now any more or less flow seemed to make the draining noise worse. I'm not sure I can get enough flow into the overflow where it would completely cover the drain without letting air get in. I can try though.

 

[hoffmeyerz]

Here's how things look right now.