Were you looking at Midnight/Volcano vs. original?
Midnight & Volcano Red are lava rock, while original is a montmorillonite clay based product. Original comes in 15lb bag, Midnight/Volcano Red comes in 12lb bags. The volcanic based substrates shouldn't raise PH, and the montmorillonite clay will mess with PH until it reached equilibrium over time.
Last edited by grizzly_a; 07-08-2015 at 01:52 PM.