Part of the patented Rowaphos production process includes freeze drying to open of the pore structure, the freeze drying can cause the raw product to release some fine material.

The material isnt harmful and is completely non toxic. Some hobbyists may want to rinse the product if using it in a filter sock or flush a reactor with a few liters of old tank water to keep the fines out of the aquarium. This will avoid the water clouding temporarily or fine material blocking prefilters.