They will colour up in a few days and settle down. I wouldnt worry about adding melafix, it wont hurt, but would do some extra water changes, good clean water will heal those fins up quickly
Just been to some LFS near me and I just saw very similar one to this about the same price as well..... I had to be physically restrained from buying him... I really want to know what they are as when I get my big big tank I want some sevs and this is defiantly something I would consider
It wasnt priced, I thought best not to ask as well because if it was affordable it would have been coming home. They had one like yours around 6 inches a smaller one that looked quite stressed at about 4. Then in the big tanks under the store tanks they had a 7 inch gold and a 10 inch notatus and my god if i had the tank for them all I would have them all.
Another update, they are both settling in nicely. I don't know if they are going to colour up any more. I am trying to work out if they are full turquoise or crossed with something else.