Hi Tourmaline! Just catching up to the new journal thread. Thanks for sharing the pics of your lovely bettas! Someday, I need to get around to posting pics of all of mine.
I wish I had some advice about Sebastian's continuing issues with fin rot. The only other medication that I can think of that you haven't tried is a triple sulfa. Other than that, I'm all out of ideas.
Bless you for saving him. Even with his short fins, he's so grumpy-faced adorable!