pool sand or play sand is slicate based (crushed quarried rock usually) and mostly for display purpose
were reef spec sand or coral sand is a mix of natural crushed rock, shells, dead coral skeletons and other dead bones ect worn away by the natural erosion in the sea making it a much more natural sand and better filter media for the reef environment
so lower in silicates and acts as a natural buffer with more neutral affects on ph ect were as other sands could and prob will change the water chemistry in the sort term or even long term use
with Uncle99 on this its not suitable for a reef/saltwater tank IMO to it might be costly over play sand but its worth it
and also the cycle process is only the beginning after that the tank has to mature over time to stabalize properly in other areas to