So I've had this cactus for years now (maybe 6 years??), and it was the first cactus I ever owned. I didn't know much about its care so it was in poor soil that didn't drain well and a pot that didn't drain well for many years. It did fine, but then I noticed that some of the roots were beginning to show recently so I repotted it in a slightly bigger pot with soil that drains better. However, it hasn't been doing to well and the leaves have taken on a reddish brown color. I'm not sure what caused this (if it was over watered, exposed to cold temperatures, is just old, or if the repotting caused this etc etc.) so any advice would be appreciated. It may be too late to save it, but if y'all have any advice on how to care for him (or any other cacti/succulents), it would be appreciated!