Overflow water level keeps rising and falling

[wvned]

What size is your tank and how much water approximately are you moving through the overflow?
In my experience the only way to make overflow drains quiet is to have 2 drains and put most of the water through a submerged drain and let only a tiny amount go through the open drain so it remains quiet.
Does your aqualifter pump need rebuilt? I have never had one but some people swear by them. I have used the Eshoppes overflows and they can fail by collecting air in the tubes that go over the tank wall.

 

[Cdentata]

The tank is 55g and my flow through is 500-600gph.

 

[wvned]

So what is the black round thing on the top of the pipe? Is it a Maggie muffler. That should be quiet.
Are you getting noise from the front box with water falling into it?

 

[Cdentata]

That is just a cap that slides over the standpipe and holds the vent tube. I believe the box itself is quiet. Any noise seems to come from the plumbing taking the water to the sump.

 

[wvned]

That all a Maggie muffler is. A cap with a vent hole. Water enters the bottom of the cap.
You could lower your flow to the sump some. 5 to 6 times DT volume per hour is plenty. How is the drain entering the sump. Is it moving air that comes out the bottom causing splashing?

 

[Cdentata]

I have attached two photos of how the box pulls water from the aquarium. The water drops down about 1 inch from where it enters the box to fall into the first chamber. It is possible some noise is generated when the water drops causing some turbulence. I'll see if I can decrease that distance of that drop.

Ok, I'll back off on the return pump speed and see if that helps.

The drain tubing makes a 45 degree turn and enters a cabinet where the sump is. Once inside the cabinet, there is a 90 degree elbow so the water feeds into the first chamber where the filter socks are.

 

[wvned]

To raise the water in the front,you raise the water in the back. Is the height of the drain pipe adjustable? Falling water in the front makes bubbles that get sucked into the siphon. That makes work for the aqualifter pump.