Chalice developed white patches?

have a 12" bubble gum chalice been growing well. I look at it last week and it started to develop white patches, did a huge water change and it stopped changing. I had some cyano show up not to long ago as well. Im about to do a 50%+ water change in a little bit. I have 4 other chalices and they are unnaffected. all acros and montis look great. the acans too. I went to get some GFO but the lfs was out. Ill probly throw some carbon in as well. I did move it to the bottom of the tank as well. 6 t5's with 3 new bulbs. any ideas?