We filled our pool about 4 weeks ago and it had some type of sediment that kept returning to the bottom of the pool. Vacuumed with extra filters-went right through. But we kept at it and it looked like we almost had it all up, so we figured we would drain it to 1/4 left to make sure it was out. We could see the bottom clearly and no trash or sediment. So started refilling and within an hour there it is again. All over. What is this stuff, is it in our pipes or something?