Thanks for the advice Andy! I really appreciate it. My filter intake is about 6" from the bottom of the tank leading into a bulkhead (And I can't move it), but I knew that wasn't the problem. The filter and all my seals seem rock solid, no place for air leaks so I cleaned the filter (including the O ring
.) After the cleaning, there was a significant decrease in the bubbles, but still a little bit. The intake was full of crap so I cleaned that as well and re-adjusted the outflow pipe and now it's completely fine. Not sure I exactly pinpointed where the bubbles were coming from, but problem solved and I've got much better flow and surface agitation now. WIN-WIN. I'll keep an eye on things just in case. And my fish are probably happy I'm not rooting around in their tank anymore.