My FC had dropped to less than 2 ppm, and I have a CYA of 0. I have been going through chlorine rapidly with sunny days. Tonight I added about a pound of CYA to one of my skimmer socks and also added 3 gallons of 12.5 liquid chlorine. I have been adding 3 gallons every other day to bring my FC up to 12 or so then comes back down by day the second day. Anyways, I added the CYA to sock, brushed the sides and skimmed the top and went inside. 30 minutes later I looked out to see the water turning yellow. I thought it must be the setting sun or something, as the water was sparkly clean when I left it. Another 30 minutes and it is worse. I removed the CYA sock. I have seen water turn yellow before on a friends pool when really high FC levels and metals in the water. I do have some metal problems (local pool clowns say maganese) with staining of pvc pipes etc, but have never seen any problem with the water color after adding chlorine, and I have had it over 20 ppm many times before, including once this year when I opened it. Do you think the CYA triggered something? All suggestions welcomed.