FWIW, you most definetly can use play sand, there are many reefers that have done this long term in the past and present (me going on 3 years). Besides my anecdotal evidence, silca sand unlike calcium carbonite sand, does not buffer the water. This means that it does not break down slowly and add anything to the water. This is because silica sand does not break down at the PH levels that reef tanks are kept. It is best to use aragonite sand to get the added buffer effect and considering that dry it is not that expensive, it is a good choice. I try to use many different colors/types/grain sizees of sand untill i come up with a consistency and color that "looks like" the botton of the ocean to me. I mix large and oolite grains, crushed coral, crushed shells, play sand added simply for astetics.