I would be very careful of Melafix. It is made using eucalypt oil, which can seriously irritate a betta's labyrinth organ. I have heard of deaths caused by Melafix. If you want to use it, get it's much diluted cousin, Bettafix, and if anything, underdose. Personally, I wouldn't use it at all. It is simply a herbal extract and I honestly think you will acheive the same results with clean, warm water. :)
My first rescue betta, Apollo, came to me in a one litre jar with no heat and dirty water, and within a few days (even after I got him into a 20 litre tank with warm, clean water) his tail fell off. There were mere centimetres left. I got it back by raising the temperature to 82F and doing daily water changes. I used Bettafix for a week during that healing period and saw no difference at all.
Your tank looks lovely - I adore Chis and I'm very jealous!