I have gerds and a hiatal hernia + barrett's from a recent scope which are all in check with a ppi should i be taking any supplements? ie magnesuim

Yes: Yes you can take any supplements you want as long as you take care of gerds , by use your ppi diet reflex prevention precautions etc close endoscopic follow up of barrett's ulcer which is premalignant , each year !% chance of becoming cancer, making it heal quickly is more important than anything else.

Supps don't helpheal: Agree with dr. Rao's answer. Supplements won't improve healing, but if you need to take supplements, then go ahead.