Many people believe that MelaFix is harmful to bettas, and recommend using BettaFix. However, knowing what you now know, you can see that MelaFix and BettaFix are the same - you will simply need to dilute one drop of MelaFix into 4 drops of water in order to have the equivilent of one drop of BettaFix. Or, you can simply use one drop of Melafix in place of 5 drops of BettaFix!
I read that melafix is actually a bit strong for Bettas that is why they have betafix.