While I was looking at the tank today, I thought..."there still seems to be some microbubbles floating around...." Not nearly as many as a few days ago, but still some.
So I decided to take apart my return pump, even though it had been completely cleaned out only 2 months ago.
Here is what I found. I believe I have located the final source of microbubbles in the tank. The intake strainer in my sump had become detached and I didn't think it would matter. I guess it does.
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400 gal reef. Established April, 2007. 3 Sequence Dart, RM12-4 skimmer, 2 x OM4Ways, Yellow Tang, Maroon Clown (pair), Blonde Naso Tang, Vlamingi Tang, Foxface Rabbit, Unicorn Tang, 2 Pakistani Butterflies and a few coral gobies
My Tank:
http://www.canreef.com/vbulletin/showthread.php?t=28436