Playsand might have silicates in it, but that is unlikely. It is likely that it is silica, and there is a big difference
Silica = SiO2 = Quartz = most sand grains = glass. NOT Soluble in water to any degree else glass tanks would dissolve.
Silicates - complex metal minerals containing Si and oxygen and lots of other things. Dark in colour, unstable/soluble to varying degrees in water. Generally dark in colour and generally NOT a component of any sands you'll see.
Most playsand is made of silica quartz. It may contain silicates, but a more likely source is your tapwater as silicates will also be dissolved into that. This is likly the source of most silicate in tanks.
Silicates are used to form diatom shells -no silicate, no diatoms. But your substrate is NOT likely to be the source of this.
Some playsand is made of aragonite, which is vaguely more preferable as the grounds are somewhat more rounded, and has some abilities to act as a pH buffer. But these are not likely to be good reasons not to use silica playsand.
Incidentally crush coral has no buffering abilities as it's largely calcite, and calcite is not soluble at pH > 7.5
