I am in the process of adding decor to my 50 gallon cichlid tank and I was wondering whether rock will raise or lower my ph? The ph in my water is low around 6.8 possibly lower. I know that mbuna need a higher ph and they like rocks and caves to hide in so I was curious as to what rocks may raise the ph? I have also previously used oyster shells to raise the ph in my tanks because it's so low. I have been looking at the reddish colored lava rock, does anyone have any experience with it?