I have a chronic low ferritin since my J-pouch surgery in 2011. At first we tried iron tablets and I was not able to sustain the ferritin levels doing that , so about 3-4 years ago, we tried iron infusion via IV, which works wonderfully. My GI doctor monitors my ferritin level every 4 months or so. If it is low, I get a transfusion of iron. I have only needed the iron transfusion about once a year, which is good. I didn't know about the low magnesium levels, but interestingly I take magnesium citrate (250 mg) at bedtime because I think it helps with restless legs. I was vit D deficient BEFORE losing my colon (good ole Seattle and lack of sunshine), so I have been on vit D tablets for many years now. I had not heard about B12 as a potential deficit. I will keep that in mind and may ask my doctor to check my levels. I learn a lot from this site and I am so grateful.