[TuKo]

Ok confermo quanto ti ho detto.Ho appena ricevuto la mail di risposta dal sig.ra Elizabeth Hiter(supporto seachem) che ti allego:
Hello,
Flourite Black and Flourite Dark are very
comparable to the original Flourite variety. They are all
specially fracted stable porous clay gravels. Literally,
the only difference is the color. The manufacturing
process and mineral content are exactly the same.
Flourite Black Sand also has the same mineral content,
however, the grain size is the only difference; it is the
consistency of sand that you would typically find at a
beach.
There is a slight difference between the
Flourites and Onyx Sand. While Flourite Black Sand is the
same consistency as Onyx Sand, the Flourites are higher in
leachable iron, while Onyx Sand is a bit higher in
aluminum and magnesium content. All are perfectly
acceptable substrates for a planted aquarium.

Praticamente l'unica cosa che hanno in comune la onyx sand e la black sand è la granulometria.Per il resto hanno composizioni differenti