I usually put all my Christmas cactus's on my porch in the same place every year with no problems. The seem to thrive outdoors. I noticed on my largest plant white "bleach" marks on several of the stems. Sort of like when you spill bleach on your jeans. These are like a very pale yellowish white on the leaves and very large. Usually two or three portions of the stem. I looked for spiders or mites or other problems but couldn't find any thing. What could be wrong? I don't want to lose this plant. None of the others seem to have any problems. ,Thanks for any help, Priscilla