Plumbing and Durso question

[NakiFantaki]

I have 60 gallon tank with a 29 gallon sump and a totally water volume of about 75 gallons. I have a single built in corner overflow and a 1 1/2 inch durso drain. I am having a small issue and I am a bit stumped. My return pump is a jebao DCT 4000 so it is adjustable. My t k has been cycling for the past month and I haven’t had this issue before now.
Today before I left for work I turned down my return to the halfway mark and when I came home I heard thy gurgling sound from the durso. Upon inspection it looked like the water level in the overflow was too low and wasn’t able to keep up with the durso. I went ahead and turned up the return pump to max and the water level in the overflow rose about an inch or 2 and the gurling sound stopped.

Not sure how to fix this problem.. it seems like like my return pump is turned down the overflow is not getting enough water..

Any ideas?

 

[Brew12]

I have 60 gallon tank with a 29 gallon sump and a totally water volume of about 75 gallons. I have a single built in corner overflow and a 1 1/2 inch durso drain. I am having a small issue and I am a bit stumped. My return pump is a jebao DCT 4000 so it is adjustable. My t k has been cycling for the past month and I haven’t had this issue before now.
Today before I left for work I turned down my return to the halfway mark and when I came home I heard thy gurgling sound from the durso. Upon inspection it looked like the water level in the overflow was too low and wasn’t able to keep up with the durso. I went ahead and turned up the return pump to max and the water level in the overflow rose about an inch or 2 and the gurling sound stopped.

Not sure how to fix this problem.. it seems like like my return pump is turned down the overflow is not getting enough water..

Any ideas?

A durso drain relies on a combination of water and air being pulled through to operate quietly. If you have more water flow you typically need less air (although at a higher velocity). To little water and you may not be able to pull enough air to make up the difference through the vent on the top of the durso. This will pull air in with the water and create a gurgling sound.

The best way to fix it is to use a throttle valve on the drain line. Your goal isn't to reduce water flow, it is to reduce the amount of air required to fill the line.

 

[NakiFantaki]

Isn’t that what the air hole on the top cap of the durso is for?

I was wondering if I should drill that hole a little bigger?

 

[Brew12]

Isn’t that what the air hole on the top cap of the durso is for?

I was wondering if I should drill that hole a little bigger?

It is what the air hole is for. I realized I wasn't clear enough. When enough air cannot get pulled through this hole it comes in with the water around the edges and makes the gurgling sound.

Instead of drilling that hole bigger I recommend drilling a second hole. One of my Durso's has 3 holes in it. The reason I like to go this route is that it is easier to block off an entire hole with reef putty than it is to make a hole smaller. I have a 2 Durso system and it runs quietest with 2 holes in one Durso and 3 in the other. Of course, I didn't figure that out until after I had 3 holes drilled in both.

 

[Gablami]

Another option is to have a cap and drill a larger hole on the side through the cap and the pipe and you can adjust the size of the hole by twisting the cap relative to the drain pipe.