a couple of weeks ago our skimmer was outputting a lot of micro bubbles into the tank which were too small to rise to the surface and just flowed around the tank with the current. The bubbles were oming out a tube near the air intake pump so we blocked it. This worked and thebubbles disappeared. Now a few weeks later and the bubbles are back. This time though they're coming out of the main output ... where the water flows back into the tank, and again just flowing round on the current instead of rising to the top.
Any suggestions on how to get rid of this?