Hey Dean,
Did you test the water he was in originally to see what was causing his
fin-rot to start? Ammonia, nitrites, high nitrates, pH swing, temp
changes etc? Getting him into good clean water was a good decision
though the fact that he began swimming funny right after the move
concerns me. You remembered to condition the new water right? And you
checked to make sure the pH of the clean water was close to that of the
old?

Swimming wobbly (head down) and not eating is a common sign of Swim
Bladder problems, but that is a separate problem from the fin rot. Swim
Bladder problems are usually caused by overfeeding or feeding dry
pellet, freeze dried or flake food. The Bio-Gold and other foods you
mentioned are only about 10% moisture and swell with water in Angel's
digestive track putting pressure on the Swim Bladder. Once there is
pressure on the bladder the fish can no longer regulate the bladder's
gasses leaving him wobbly. Once that pressure is relieved by a bowel
movement, everything should go back to normal. Give him a day or two of
fasting and see if this helps. Also you can try to give him a small
portion of blanched pea or daphnia as a laxative if it doesn't clear up
in a couple of days. In the future, consider altering their diets to
more natural foods like live or frozen foods. Swim Bladder problems
don't cause any pain to the fish, but it can make it difficult for them
to reach the surface for air. Adding the air-stone was smart and also
maybe throw in a plant or two so he can rest near the surface if you
find him having trouble getting his head up to breathe.

Now, back to the fin rot issue. If he's lost more then 1/2 - 2/3 of his
tail I personally would medicate. Jungle Fungus Eliminator or Maracyn 2
are good antibiotics or in very serious cases where it's reoccurring or
combined with other problems like septicemia you may need a strong
antibiotic like Kanamycin Sulfate. Make sure to follow the directions
on the package and whenever you begin an antibiotic be sure to finish
the entire course so as not encourage bacterial mutations.