Since Melafix is "all natural", so you think it would react with it if there were traces of another medication in the tank and I treated with it? Really long story around this one, anyway let's just say I don't have carbon.
Just because its all natural doesnt mean that it shouldnt be treated like any other medication. I would think that it could react with other medications. Unless of course the other medication is made by Aquarium Pharm. All of the meds made by them can be used concurrently.