Review on Red Sandstone Metamorphic Rock Specimens by Shawn Reiter

I know this is intended as a teaching aid but they also work great if you are having trouble raising the pH in your home aquarium. I put two rocks in a 5 gallon freshwater aquarium and it raised the pH from 6.0 to a neutral 7.2 in a matter of days and stabilized for two weeks even without changing the water. Highly recommended!