My zig zag (aka fishbone, aka ric rac) cactus seems to be dying. I kept it in the same north facing window for about a year and it was completely healthy until about a month ago, when it started getting dark spots on the leaves. I thought it might be root rot, so I repotted it to check the roots and they looked completely healthy. It’s in a cactus mix combined with about 25% coco coir. Since then it’s continued getting worse, more dark spots and portions of leaves (and some entire leaves) turning yellow, then brown and soft. I’ve been cutting off the leaves as they die, but I don’t know if there’s any saving it. If you have any ideas, please help!