Have a customer who had really low ph and alkalinity in his 18 x 36 in ground pool. Never added and sodium bicarb in years. He went through many pumps over the years. Well I had him add 40 lbs of bicarb. He says a day later his entire pool liner and steps turned grey and will not come off by brushing. What could this be? He thinks it because I had him add the bicarb. But I dont see why that would do it to the liner. HELP!!!