Dorso Pipe

According to the Durso website, it sounds like you have the "flushing effect".
How deep is your drain line into your sump?
It should be about 1" below the water level so there is not a lot of back pressure, anything deeper will cause the water level in the drain and raise and lower in a rhythmic cycle.

 

That makes a lot of sense, my tank is 24 inch height for a standard 90G. the water is 2 inches below the water line in comparison to the drain chamber. I didn't take this into consideration and thinking I wanted it hidden under the tank and not poking out. Looks like I could try that and add another inch of pipe into the drain and see if that helps. Although it seems to be doing fine right now, with a lower return flow into the tank

Thanks for your help

 

My aquascape

My aquascape : )

 

The airline tubing may only need to be lowered down 1" or 2", it all depends on the water level in the overflow box. I find it will usually be about the same distance down as the surface of the water in the overflow once it settles down. As little as 1/8" can make a huge difference so adjust it up and down in very small increments and very slowly so it has time to adjust. It usually is very dramatic once you find the sweet spot.

 

"It usually is very dramatic once you find the sweet spot."

That's what she said! Sorry couldn't resist