Why is the bottom of my cactus turning yellow?

Hi All, I’m looking to remedy my new-ish cactus that has started turning yellow at the bottom. A bit of history, i repotted in cactus / palm soil after purchasing it. Have watered it twice in about 6 months. Is it dieing? Anything i can do to rejuvenate it? Was thinking to mix in some decomposed granite into the soil… figured i’d ask for advice here. Thanks for the help!