It’s difficult to follow despite the fact he speaks painfully slowly. He probably thinks he’s making a point and explaining something but he isn’t being specific enough in his statements and the result is meaningless drivel. What is softened water, why is it special, what does it contain?
What minerals have people been using? There’s a lot people can add. Some sachets might not be suitable for espresso machines and others will be. In terms of thin films they can be made of up of a lot of things, silica, sulfite, carbonate. Or oxide layers. I’d be amazed if an oxide layer could form that would be susbstantial enough to cause overheating. The thermal sensors (stainless steel) hopefully have an oxide layer on them that prevents corrosion….what’s the oxide layer that forms on chromium oxide?
I’ve seen the video in the past and IIRC the guy is also selling water treatment options to soften water which just about tells you all you need to know.
He may have seen issues with people adding Magnesium salts e.g. epsom salts and sodium bicarbonate to remineralise water in the mistaken belief it won’t form scale because “Calcium causes scale” or something along those lines. He may also have seen issues with people using service boilers with their special water that “doesn’t scale” without realising the minerals will concentrate in there. etc