Hey, so I just picked up two bags of "white Lightning nepheline syenite" it was sold to me as pool filter sand at a pool store. So far I have washed a 50 pound bag of the sand until the water ran clear. The sand is white with black flecs. My question is is this brand safe? It doesn't say anywhere on the bag that is it meant for pool filters. I found this link, I am thinking it is meant for sandblasting?? What is the difference, also this says it is "low-silica" Is this safe to use in my new 75 gallon tank?