Have used BBB method for years but have been fighting a metal stain on my white fiberglass steps and even liner for years . Readings are FC- 3.6, PH 7.6 , ALK 126 , Hardness 280 . If I sprinkle Abor. Acid they disappear for 10-14 days . Use Kem Tech algaecide . Heater . City Water . Could it be the algaecide and do you have a recommendation ? Any other thoughts ? Hate to use the Abor Acid as it impacts the water readings but dont know what else to do