Silicate sand has no buffering capacity, Coral based sand is full of calcium, will help keep your ph swings down and is part of their natural environment for a reef setup. There are 100's of articles on this subject so i won't go into big detail on it. Bottom line is silica sand will work fine, you can get it at your local walmart for cheap, it will not harm your livestock unless you don't know the source of the sand, then your just playing roulette at that point. In my opinion I am all about replicating the corals natural environment and would do what i could to make it that way in as low stress of a change as possible.
Stores that dabble in pond / freshwater etc sell it. but i've not seen any at the salt only stores. but i don't shop everywhere either.