plumbing issue

[terracereef]

I have tried everything I know but to no avail. My system is a 400 g with center overflow. the two drains are 1.5" with the returns being 1" each. Return pump is a Hammerhead/Barracuda gold hybrid. The sump is directly beneath the aquarium in the basement. The issue I'm having is microbubble from the drain. I have to valve down my return pump around 40% to reduce, not eliminate, the bubbles. I've increased the size of the hole in the 90 on the drain but didn't help. Any ideas what might be causing this?

 

[redfishbluefish]

What immediately comes to mind is a reverse durso in your sump. Let me see if I can find pictures to show you what it looks like.

 

[mehaffydr]

How big is the sump? Is there enough time for the bubbles to dissipate before being pulled into the pump and returned to the tank. If the sump is small there may just be to much turnover in the sump volume.

 

[redfishbluefish]

There are a number of reverse durso designs and this is the one that worked best for me:

Although it worked to eliminate the bubbles, I couldn't fit this in my sump with a filter sock.

I talk about using this in THIS THREAD.