But the assumption is that all of these parameters matter, and that there are forces at work pushing these parameters towards undesirable levels (wether too high or low). And even if that's the case, I still don't see how sending out a test several times a year and then specifically supplementing each of these elements to "correct" values which may or may not matter is easier than just changing some water every once in a while... I guess my issue is, I don't see the problem that we are trying to solve. Everyone has their "reef idols", whose tanks they are trying to emulate... as far as I know, none of the tanks I drool over are individually testing and supplementing cobalt, nickel, vanadium, boron, chromium, sulphate, bromine, etc. Individually testing and supplementing each of these can't possibly be simpler or cheaper and certainly doesn't have the proven track record compared to just changing out some water?