The white fin tips might be new fin growth. I see something similar on my red CT's. Freaks me out sometimes.
Clamped fins are usually one of the first signs that something is wrong, however that does not always mean the betta is sick. I got one guy that has been badly clamped all summer and I have medicated him for everything you can think of and no one seems to be able to tell my what his problem is - Not even Sakura
What worries me is not the clamped fins but that he is not eating. Are you sure the ick is gone completly?
If it was me, I would:
1) ditch the filter. Since you need to do at least 2 water changes a week anyways, the filter is just taking up valuable space. SOme people say tanks under 5 gallons can be cycled but, eh - to me, it's not worth the hassle. Plus most hve to strong of a current anyways.
2) Do a 100% water change and clean out the gravel to remove debris. From what I understand, you have already done this, yes?
3) add in a hiding place and plant that reaches the surface, even if its one of those cheap plastic tetra water wonder plants. If you remove the part that goes into the gravel, it will float at the surface. I suggest this because my guys LOVE to sleep in some kind of floating plant at night- weather it's a real plant or a fake floating plant.
For water changes, In MY opinion - I think every day is too much (unless he is being medicated). OFL suggests 2X a week even for 1 gallons. One 100% with gravel cleaning and one 50%. Maybe add in an extra 50% change if you want.
You are using water conditioner, right?
And yes - epsom can be used as a ferterlizer. I seen it on the directions and was like WTH?