So after some long and careful thinking I have decided to turn my tiny 29g into a Rio Negro Biotope. Upon doing research, and watching 4 documentaries on the amazon river I have narrowed the most accurate substrate between these two. I would just like to know which one of these two in your opinion would look more accurate in terms of replicating the amazon river. Oh, and also are both safe for aquariums? I don't want to put anything in the tank that could potentially alter the water chemistry.