Help...what could this brown dust be and how to get rid of it? I have a brand inground new pool with a salt water filtration system it has been open for 4 weeks. The water is crystal clear and chemicals/salt lever good. I have a sandstone liner and in the shallow end you can really see patches/aeras of brownish dust. It is not spotty or dark, just a faint brown film. I use a Polaris vacume every day but this does not pick it up. However once I brush, it disapates and is gone. But comes right back, I have to brush every day. The dust is also on the side walls of the deep end. Any suggestions to get rid of this?