Microbubble Problems: Need Advice

[ron101]

Hey guys, still messing around with my first sump system and need some advice.

I have 90 gal RR and have been using the durso setup and 1-3/8" ID overflow bulkhead that came with the All-Glass overflow kit. The return pump is an Eheim 1262 (900gal/hr at 0').

With this setup I get tons of air and turbulence into the first sump compartment. I pulled out the durso and put in a smaller bulkhead and ran it bare (no overflow pipe since the durso wont fit the smaller bulkhead) to smaller diameter tubing to the sump and there are no bubbles whatsoever and no flow rate probs(of course the overflow box is now way too noisy).

Would I get a similar reduction if I installed a smaller diameter durso and kept the smaller plumbing or is it the durso itself that introduces the air? Any other design suggestions are also welcome.

TIA