The contribution of calcium and alkalinity to an aquarium through the dissolution of Aragonite would be indicative of significant problems as it requires typically a pH of around 7.5 to become available - whilst this happens in a still sand bed as depths increase (as Oxygen decreases, the acidification of the sandbed increases), the rate is both insignificantly small, and not very available to the water column. In-situ dissolution is a rather ineffective means of providing buffering (and a rather expensive one compared to the amount you'd spend on raw elements to substitute it).
As VaultBoy said - whilst Silica solution has been linked to an increase in Diatoms, again, the pH level needed to dissolve crystalline Silica is much lower than any healthy aquarium will ever experience. Wash it well and you'll be fine. I've used it several times in the past and actually found it to be generally superior to Calcium-based substrates as it tends to bed together better allowing for higher flow rates, and also tends to maintain a much cleaner appearance. Plus... it's significantly cheaper and generally much whiter in appearance. The only negative I found is the benthic invertebrates were slightly less than with a Calcium substrate by virtue of the crystal structure... but, that isn't the be-all and end-all of a sandbed.
Personally, I'm sick of Calcium substrates. They're a pain and expensive to boot with little real-world benefit. Choose what is important to you from a sandbed.