I am playing with my diet to see what works for reducing BF but not weight.

I swim a masters program (average 1700-2000meters in 1 hour) 3 days a week, walk/run 2 days and do a tough hilly 10 mi bike ride once a week.

As I understand it, I should keep my carbs low (50-60g range) and my fat higher on my swim days and increase carbs while decreasing fat on my run/ bike days as those are higher exertion work outs.

Does that sound right? What about my day off? How should I eat then?
Again, just trying to maximize fat loss!
I am :
46 yr old female
121 lbs/27% BF