A nice example of an overcomplicated setup.
Ozone is connected to the skimmer, and I have been looking for an airpump to increase the airflow through the air dryer into the ozone generator since it is significantly below the recommended value of 8 /10 (according to Ozotech inc) - currently around 3/10.
It appears now that the airpump pushes too much air into the skimmer (even though it is still below 8) which creates this effect. With the airpump turned off, this goes away.
Therefore, no airpump for the ozone generator.
Correction: Retained the air pump setup but it will auto shut off when the skimmer shuts off, which broadly resolves this issue.