Although the substrate says it will raise pH 8.2, is that sitting in water without fish, or supposedly with fish.
Aragonite would be one such substrate that buffers acids, and maintains equilibrium.
But metabolism in itself from fish waste, and other biological processes producing uric acid, etc, will naturally lower pH.
Tannic acids from waterlogged wood pieces will naturally lower pH a bit.
What kind of fish are you keeping, and how many and what siz,e that you are worried about an 8.2 pH?
The more fish, and the larger types will produce more acid, and buffering it is a plus.
If you are keeping Amazonian species that are healthier in pH below 7, than rather than mess with the acids you would need to counteract the buffering capacity of the pH raising substrate, it wouldn't it be much simpler to just get and use an inert one?
Most common aquarium substrates available are just that, inert.