Day 12 - Monday 9th - Around 8:30pm
Just cleant the mechanical filters. Apparently no more bubbles. Therefore, I will wait until this next weekend before modding the pumps... I know... I am a bit lazy
The skimmer has got quite a lot of unfiltered water during the filter cleaning and skimming has completely stopped. I will check if that happens again before jumping on conclusions.
GrandeGixxer: yes, agreed. That was the plan.