I needed to replace the sand in my filter so I went to a local pool supply store and bought 6 50lbs. bags of sand. I replaced the sand, back washed before running the pump/filter. I noticed a layer of fine sand on the bottom of the pool. I looked on one of the bags of sand I bought and no where on the bag does it say for use in swimming pool filters. In fact it say "When included in material grade number means ARB Certified for permissible Dry Outdoor Blasting". The first line on the back of the bag "Blasting sand contains fine silica dust".
I thought I was buying pool filter sand. The "fine silica dust" explains why I have sand in my pool. Why would they sell me this sand?