ok, this has got me all confused. i think im almost ready to get my first shroom or polyp of some sort so i think its about time that i truly understand whats going on. ive read alot of things that say something about magnisium, iodine, and other stuff. theres also calcium to test for and all this stuff has got me all confused

. so my question is, WHAT ELEMENTS AND COMPOUNDS ARE IN A REEF, such as magnesium or iodine and calcium, THAT I WILL NEED TO TEST FOR AND POSSIBLY SUPPLEMENT OR ADD TO MY TANK, AND WILL DETERMINE THE HEALTH OF MY FUTURE CORALS, SHROOMS, ETC. it would also help if you could state whether the element or compund is good and needed by the corals or if they will hurt the corals and should be avoided. thanks