What is substrate ? It is the material at the bottom of your tank.
There are many type of substrate to use in the volcano shrimp (opae ula) tank.
I prefer natural substrate over artificial substrate.
I am afraid of colours or chemicals leaching out of artificial substrate into the shrimp tank, killling all my volcano shrimp (opae ula).
My favourites are lava rock, lava chips, coral chip and coral sand.
Coral sand contain calcium carbonate and it is good for shell or exoskeleton of the volcano shrimp.
The small lava rock chips provide many hiding place for the volcano shrimp (opae ula).
Seachem also sells a wide range of natural substrate. There are many you can choose from, such as:
a) Flourite Black Clay Gravel
b) Flourite Red Clay Gravel
c) Fluorite Black Sand
d) Onyx Sand