Faecal transplants have been shown to completely cure colitis, but medicine is resisting them, so you’d be lucky to find somewhere to get one. Colitis is linked to a variety of bugs, so I wouldn’t assume it’s candida without a better diagnosis. It’s a pretty serious issue, and blood and diarrhoea probably indicate a flare up. You can assume it’s dysbiosis of some kind. Diet and probiotics may help if it’s confined to the colon. I’ve heard good things about the Specific Carbohydrate Diet and GAPS diet for colitis, but I’m not sure if it provides anything over than symptomatic relief. Hasn’t he had a stool analysis or other tests to give you a better idea? Seems like he should see a doctor in any case.