Adding vitamins to the water does very little, if any at all. You need to enrich the bbs with vitamins, selco, or spirulina powder to do much good. You can also thaw frozen foods in a couple drops of liquid vitamins, but they need to soak in this overnight for it to be very beneficial. Selco is a HUFA..(High Unsaturated Fatty Acids)
Enriching BBS is a very good way to boost the growth of fry. My last 2 spawns, i used Selco and Spirulina. The growth rate almost doubled in the first 2 months. If enriching bbs is pinned somewhere, let us know...If not, I'll make a new post on it.