I need sone advice on my succulent-cacti garden that i purchased from BJ’s please. Two leaves fell off and there is some brown stuff on a few leaves that i can’t scrape off initially initially. I put it under my stove light and when i tried to remove the brown stuff later on, some of it came off along with a cacti leaf. I’m not sure what to do now. Photos below (starting with the healthy, just purchased pic of the garden). thank you!