I might be wrong but sometimes diet isn't enough to replenish vitamins and other food nutrients for some of us. Also some people who are floxed may still have an infection on-going and cannot eat certain types of foods that could worsen their condition.

For instance, I cannot eat oranges to get Vitamin C because they are sugary fruits and since I have a bacterial prostatitis they could worsen my condition. Another example is that some people here are anemic, so getting iron from simply eating pork and beef isn't enough in some cases.

What I'm trying to say is: supplements in most cases are okay to use but the most important thing to do is to not overuse them but also to not use too many of them at the same time. In that case, they would kill your gut flora just like a fq or any other type of antibiotic would.

Of course, if supplements do create problems (like in your case, unfortunately) the diet is the only other viable option. Although I think that changing your diet while also taking specific types of supplements (such as the ones containing magnesium only) is the best option in most cases.