It’s an inorganic microflocculate bioclay. 

When you dose it into your tank, you’re going to notice it clouding up for about 4-6 hours (so dose it at the end of the day).  Afterwards, you’re going to notice a significant difference in water clarity, especially for tanks with yellowing or hazy coloration. 

This is because the particles in the tank are latching on to the bioclay in the Coral Snow, which builds them into large enough clumps that they can then be removed by the skimmer. 

The other crucial thing to know about Coral Snow is its ability to bind to other additives, as well as the mucus membrane of corals.

By mixing it with other additives before you dose it into the tank (mixing it in a cup / bowl / etc for a couple minutes before applying it), the flocculate will be able to absorb the additive like a sponge. 

When you then dose the mixture into the tank, the additives, having bound to the clay particles, will be able to attach to the mucus membrane of the corals. 

This allows the corals to consume them directly when they consume their mucus membranes, instead of having to rely on obtaining it passively through the water column.

This can have a dramatic effect for several additives.