Ok you are so close, here it is:
It is F.) none of the Above, but: The Stone connected to the Airpump laying in the Solution was a cheap Stone with Calcium-particles in it. This caused a super rapid fluctuation.
Why did I do this Letter mystery thing? To show some how wide spectred the world of growing and knowing is.
And this goes out to especcially the newer grower: Don’t trust any opinion on the internet. Make your own Experience, before trusting too much nonsense, maybe the Grower could have saved a lot of Money and time by just trusting his own believes.
(I feel you Thierry. ;))
Be well everybody. I hope you can take it with a smile.