what I have read is silica sand in inert and the glass that the aquarium is made of is aqually or more so likely to cause a diatom bloom. Silica is not silicate just like calcite is not aragonite yet both are calcium. the only thing I've heard about silica sand is that there is no buffering and that it is too rough for the little critters. But in my FW
tank my fish eat it and is passes right through and deeper protions of a deep sand bed don't have any water flow to it (that being the point of it) so those layers of aragonite wouln't be doing any buffering anyway, only the top couple of inches would buffer the water by dissolving. Yep, I've talked myself into doing my idea hope it works alright in the long run.