No matter how well you design and construct the parts of your setup, you always find a few problems or issues you have to tweak. Here are things I had to modify.

 If you have already looked through all the sump pictures you may have noticed a difference in the refugium drain pipe. In my original design the pipe was cut off directly below the drain pipe bulkhead. I thought that water partially filling up the drain pipe would prevent bubbles from developing below the refugium. This would prevent me from having to angle the refugium bottom, and would make less noise. WRONG! When the water filled up to the height of the right side waterfall baffle it also partially filled up the refugium drain tube. This leaves several inches of air between the water level and the drain tube top. I didn't realize this would only cause a constantly trapped air pocket in the pipe.

 Although, it makes a great aerator, it causes bubbles to develop below the refugium. Every few minutes it would burp from underneath the refugium up to the baffle. The pressure change from the burp caused the trapped bubble inside the drain tube to be sucked out making a big slurp noise! This was bad, every few minutes IT SOUNDED LIKE SOMEONE FLUSHING A TOILET! Here is a picture of the bubbles developing below the refugium.

First, I tried installing a dorso style drain and some other configurations on the top of the drain tube. This effected it a little but only increased the amount of time it took before burping. I then decided to drain the right side of the sump and install an elbow and extension pipe. I had to drill a hole in the unused bubble trap wall between the refugium and right side bio ball section.

I then cleaned up the shavings and installed the elbow and extension pipe.

This worked great! It kept bubbles from forming below the refugium, made the drain pipe silent, and released a smaller amount of bubbles underneath the bio balls. Bubbles below the bio balls can only help. Here is the after picture.