sorry to hear about fred
well when my betta Rosalie got fin rot, i did a huge wc and added stresscoat. now she is recovering
when my betta Luna got fin rot i tried bettamax but the winning meds were "lifeguard"
also, my bettas likes salt and it does help their recovery, i added salt when i treated some of my bettas for ich and now they are healthy happy little buggers!
I hope fred gets better,
and hope this helps!