a calcium supplement and an ALK
supplement are what i would suggest, if needed of course. using a "reef" grade salt mix and doing regular water changes usually covers this unless you have a large coral load as stated above.
i would think if you needed a ph buffer, you don't have proper gas exchange, and can correct this with more surface agitation.
i have never added vitamins to any of my tanks and have never had ill effects, except for one time when i was early on and added a squirt of "kent coral-vite" to a 100 gallon system (that was doing fine) and overnight all the corals declined. it took me multiple water changes to pull that crap out of the tank and now i always tell folks to never
add anything you can't test for and aren't sure you actually need it. in many cases, it can do more harm than good.
, you can put a 6' protein skimmer on a 50 gallon tank and not pull out enough vitamins to matter to your livestock. to date i have not seen any data disproving that.