Pro Shrimp's comment: Mineral stones keep releasing minerals into the water (constant low amounts, which do not affect the water parameters by much), supplying bacteria and microfauna with a constant stream of needed minerals. Additionally these stones can absorb toxins and polutants via ion exchange, thus improving water quality directly and indirectly. We have these stones in most of our tanks. Shrimps love to graze on these stones. From time to time it's advised to give the stones a little clean with an old toothbrush to remove algae.
Helps maintain good water quality by absorbing harmful waste
Enhances the colour of shrimp and fish, especially whiteness