Vitamins will do your fish good. Just ensure they're FISH vitamins. Multi-vitamins, for people, are based on daily requirements for the commercial anatomical average. That means the concentration of vitamins are measured for a person that is 5ft 8" and 150lbs. Get yourself the proper supplements for your fish. A product called Vita-Chem will offer your fish vitamins and trace elements that are lacking in a captive diet regimen. This product is available in FW and SW formulas.