Micro Bubbles

I have micro bubbles in my 58 gallon reef. Yesterday, I tried to get to the cause of them. I turned off the skimmer, still had bubbles. I turned off the refugium water, and they were still there. I switched to a different return pump. Still bubbles.  I see bubbles coming from around the pipe that brings the water from the tank to the sump. This is PVC coming down in an L shape. It has two 90 degree elbows and a down pipe straight into the sump. I have it going into a water bottle cut off at the top to help reduce the blast effect, but I still get bubbles.
How SHOULD i be taking this into my sump to avoid the bubbles that must be getting chopped up by the pump and returned to the tank?
Thanks for any advice here. I don't know that I've ever looked at anyone's feed to their sump; I just made it up as I went.

 

Have you changed or added anything recently?

You can try turning down the output of your return pump to see if that helps.

 

Its possible that your sucking air somewhere in the fittings between your return pump and the DT. Also a simple high low high baffle system between the Skimmer section and the return chamber of your sump will help big time.