Planted Tank Obsessed
Join Date: Jul 2009
Location: orange county, CA
Fizz does not mean the substrate will be leaching Ca or Mg ions, it could mean that the mineral is able to absorb water. For example, Calcium Bentonite is neutral but when i put it in water it fizzes and change color, but its actually absorbing h20 and metal ions in the water, lowering the PH.
The only way to find out is to put some of those rocks in a cup with distill water and see if it changes Gh Kh or Ph overnight.