Water chemistry remained the same for me, but you have to rinse it out VERY well. It is a very dusty product.
When I rinsed mine I filled a bucket 1/4 full with it and filled it with water. When I stirred the sand around, the water turned black, just to give you an idea, and also turned my hand black (rinsed right off though).
I just upgraded to a larger tank and added more of this. I can test the water when I get home and let you know if anything has changed since I added it 3 days ago to an already established tank.
BTW my friend is also using this in his cichlid tank, and planted on of my brazilian pennywort stems in it. No ferts, co2, low light, and he says it has actually started to grow rooted, which mine won't even do in my high tech planted tank. weird.