Ahhhh, the eternal sand question!
There is sand and there is sand. It's best that you learn what is proper sand, so that you can regognize it, since the quality of sand varies from locality to locality.
The sand you want is pure silica sand. It must be salt and mineral free.
Quartz sand should be pure white, with no multicolored grains showing. These other colored grains may or may not be quartz, depending from where the sand was mined, but as a good rule of thumb multicolored grains should be suspect.
Initially, this type of sand is fine because the detrimental elements are bound up in the chemical composition of the mineral, but the acids in the peat react with these minerals, making soluable salts which are not good. So, after a season or so, the plants can decline in health as these salts accumulate. This is especially true if the grower does not occasionally top water the plants in this mix, since the salts are accumulated at the surface of the mix by evaporation.
Even pure white sand cannot be completely trusted. A good plan for those who REALLY want to know, would be to take a small teaspoon sample to a local Pharmacist and politely ask if he could apply a drop of strong acid and let you know if it fizzes. Alternatively, you can also test with clear vinegar, but the effervescence is not as noticable so you must be very observant.
The grit of the sand is also a consideration. Sandblasting sand and "play sand" are very fine grained, and so makes a very dense and compact mix when they are found to be suitable. Generally, I use it only as an additive in some mixes, and never 50%.
Pool filter sand is of a coarser grade, but here again, there is no industry standard. I have seen the pool filter sand marketed by Walmart and (at least in my area) it is not suitable. Look for a ssmaller business concern for pool filter sand, as I suspect Walmart does use a large volume distribution of this product.
White pool filter sand is very clean, and coarse, like granulated sugar. I still rinse it until the water runs clear, but I get far less algae and moss problems with the use of this vs the finer graded sand.