@Ben: While I am making strides with the DE as Michael is, I did add a dose of Natural Chemistry's Metal Free into the water.. ( this is one of very few items I buy from the pool store)... it has worked like a charm the past 4-5 years....This years dose (which was yesterday) has yielded no results... I dropped FC to near -0- and PH in the 7.0 range..... (( Alk is 110 )) Any idea why this didnt take this time around... ? (the stains DO disappear with the Vit C powder)