Not from Craigslist but... Will not affect water chemistry, but then states that it may raise pH. Huh...
"Designed specifically for use in freshwater aquariums, gravel will not affect water chemistry in any way, and provides a great place for beneficial bacteria to colonize. Whether you’re looking for a bright substrate or something for your natural tank, pure water pebbles are exactly what your tank requires. May raise your tank’s pH"
Some people like cucumbers better pickled