It is natural river gravel. Unlike sea gravel, you do not have to worry about hardness increase.
There are 4 size variety, S, M, L, and LL. S size can also be used as substrate material like Oiso sand. M-LL size can be mixed together, and used for promoting riverbed aquascape.
$15.00Nano Shrimps Gravel Bed, Arkansas Grey
Dennerle Crystal Quartz Gravel. Perfect bio-functionality and highly attractive as well.
Rounded grains protect bottom-dwelling fish.
ADA substrate additives are to be sprinkled on the bottom of the substrate layer, or on top of ADA Power Sand. These additives help to make a stable and healthy substrate in a newly freshwater planted aquarium setup.
Special re-packaging (different from picture shown) in pre-mixed set specifically designed for 1.5 - 2 ft freshwater planted aquarium setup comprised the following special formula: