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.
IMO, 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.