Hi Keith,
Thanks for pointing me towards that video. There are a few key statements in that video:
"And we don't have Seramis.
I never handled Seramis. ... I don't know anyone with Seramis. I don't want to buy Seramis. It's expensive in Europe. It's even more expensive in the US. And then I'd be left with that expensive thing I'd never use." Well then... he's arguably not in a position to judge this material. And yet, he does. As he tries to frame his reasoning in some pseudo-scientific rationale this is laughable to actual scientists (see below).
Then, there is that weird transition that seems to suggest that ceramics(!) in general can show organic growth on them. Well, sure. As far as I know that's well known with Terracotta pots as well. How that leads to the prediction at the end of the video that using Seramis may lead to moisture problems (but none of the other materials cited at the beginning of the video which are also various forms of ceramics) is beyond me.
And he states that "I am not a chemist" but then he tries to extrapolate from a calcination process of one clay type to another. That's quite... bold. Note, I am actually a PhD Chemist. For instance, his statement that kaolinite contains "crystallised water" clearly shows a lack of understanding. The formula for kaolinite actually lists OH (hydroxyl groups) and not H2O (water). There are minerals that contain water (H2O) as part of their crystal structure. But the hydroxyl groups (OH) in this clay are largely sitting at the surface of the clay particles. These surface hydroxyl groups are part of the reason why clays can be semifluid because they interact well with water. But that's water between clay particles not inside of them. In a calcination process, hydroxyl groups from one clay particle react with another eliminating water as a byproduct and forming an oxygen bridge between the particles, essentially fusing them. Hence, the dehydration(!) and densification of clays in firing yields ceramics. This is of course grossly simplified.
Anyway, that Seramis might be an overpriced version of Turface Athletics (again, there is actually no evidence in that video. It's just conjecture.) may be true. But it's also irrelevant as I am in Germany and I haven't seen such Turface product here. And the Seramis product is the closest I have seen available in stores in Berlin in small quantities that resembles in structure the substrate I see in a lot of photos on this and other forums.
That being said I learned today about Uhlig Kakteen in Southern Germany. And they indeed offer premixed soils as well as the individual soil components (perlite, pumice etc.) for cacti in small(er) quantities. But their delivery times are 12 - 20 business days...
I have no idea if Seramis is a good or bad substrate for cacti. That's why I asked. But that video is a hack job. Best.
I really don't have the need nor the space for that much material.
it's the internet