Have you considered setting up a QT, or hospital tank ? All of us should, but many of us don't, and right now that includes me too, the QT tank is full of shrimp, and their new home is months away from being ready.
But having one is a good idea. If fish you buy have anything wrong, you find out before they take their issue to the main tank, and it's easier to treat in a smaller tank anyway. Easier to observe the fish in a smaller tank too, or at least one without plants or decor in it. QTs should be pretty minimal, to make it simpler all around.
I agree Melafix is not very useful... that seems to be a common opinion I see on it. Usually, if water is discoloured, activated carbon will remove it. It is one of the three things carbon is useful for.. colour, odour and med removal.
So if you don't have carbon or it's been there for awhile, replace it with new and hopefully, it will take out the colour. Floss is good for water polishing, so if you don't have floss in the filter, adding some may help clear the cloudiness.
Water changes obviously, possibly quite large ones. You can do two or three changes back to back and change out all the water that way, but with less stress for the fish than trying to drain all the water and replace it in one go. You can wait an hour between changes to make it less stressful, or do them fairly quickly, if, for example, you had a nitrite spike that needed to be dealt with right away.