If you are talking about a vitamin supplement to add to the water, I dont think any of them do much of anything at all. There is virtually no evidence (outside of a manufacturer's claims) that fish uptake vitamins out of the water. The solution is to feed them a variety of food and make sure that they are getting all that they need. Most processed foods are vitamin enriched, and the list is usually on the container -- so, a combo of processed, fresh and frozen foods should deliver plenty of vitamins.