ZZ Plant Diagnosticians Needed! One shoot @ a time, leaves yellow, usually from the tips to the stem, then the stem goes soft and I cut it away. It has been small young stems until now and now it has struck a large older stem. I have a 24 high ZZ plant, bought about 1 year ago from a reputable greenhouse/nursery in the area. It seems it is always putting out new healthy looking shoots, but one by one I notice another otherwise has been healthy shoot begin to look a pale green, the leaves yellow, but only on that shoot and gradually the shoot begins to look shriveled and soften a bit. It started last summer so I put it outside to see if it needed more light. It seemed to not make a difference and continues. I took it out of its plastic pot ( 8 Bottom Width X 9.75 Top Width X 8.75 Ht.) it came in. It had a large root structure from the tubers, some fit tightly against the plastic perimeter of the pot. I gently took the soil away and trimmed the roots of a few (3) that seemed mushy at the end of the tip, and removed others that seemed like they were a wet flat fleshy thread that may have been a root and slowly seemed to decompose. A better description would be like a limp flat off-white intestinal casing and these seemed to just pull out of the root structure with ease. One large tuber seemingly connected to the now yellowing large stem seemed to be softer, shriveled and not looking as robust as the others. The original soil it came in was a mixture of soil, pearlite and much bark. As for watering, I hardly water it. I was told to water lightly once every 7-8 weeks. I took the plant to the place I purchased it and they said, maybe re-pot it, maybe a little bigger pot, and maybe new soil. I found them less than helpful. Any suggestions?