Marine pure, brightwell, maxspect, and matrix are all amorphous aluminum silicate aka “pumice stone”. Despite what anyone on here will claim or argue, the data is out there on the manufacturers sites if you look hard enough. The aluminum silicate powder is formed differently by each brand, so the pore structure and overall hardness won’t be equal across the board. But the chemical makeup is the same. Having heard constant complaints of marine pure and brightwell breaking apart to dust quickly, and not hearing that as much about matrix, I went with 4L of pond matrix. It’s surface area is greater than the others as well...and it’s cheaper. Why isn’t it used more? Likely because people tend to buy what bulk reef supply tells them to (and don’t get me wrong I love brs and order from them monthly!), but people tend to look one place for advice and take it without research.