Betta Prognosis????

[Kitekat87]

My betta, Roy, has fin rot :-(
He has been really lethargic and lost quite alot of his fins overnight. He is currently in a 17 litre tank with a filter and heater. I did a 100% water change today and added melafix and 3 teaspoons of aquarium salt. I plan on doing another 100% water change tomorrow, redosing the melafix and upping the salt to 6 teaspoons.
What do you guys think of his chances?
Is there anything else I should be doing or not doing?
Here's a pic of him today

 

[Kitekat87]

Day 2
Done another 100% water change, upped the salt dosage and put some more melafix.

He has lost more of his fins and looks worse today. He's have trouble swimming now, he just keeps floating to the top. But on a positive nite he has eaten some food and even seemed a bit excited.

Today's pic