FWIW, I've never seen any clear evidence that corals benefit from vitamins dissolved in the water, and if so, which ones or how much might be useful.
Many "vitamin" products sold to reefers have so many different types of things in them (trace metals, amino acids, carbohydrates, potassium, fatty acids, etc.) that one cannot draw conclusions about what was useful, even if the whole product is thought to be useful.