Eb0la11's 165G Reef Tank Build

[Eb0la11]

Hey guys, I got another problem that is puzzling me. I have tiny micro bubbles being injected into my tank from my four returns every two minutes or so. I have no idea how any air is getting into my return line. My sump also has no bubbles whatsoever in it, so its not occuring here and the pump is not sucking in bits of air with water.

Any idea why its still going? I thought perhaps itd stop after a while of running, but its been like 48 hours. It cant be just loose air bubbles still in the lines. Anyone else have this and maybe know what I could look at?