DelfinT wrote,
Today I found out my favorite fish "Jackie" ( I would like to think
she is a girl) has hole in the head.
She has not lost her appetite & is behaving normally except for
sometimes trying to scratch herself on the driftwood....

If that's the only symptom, it doesn't sound as if it could be
hole-in-the-head (HITH) to me. For it to be HITH, it would have to have
pin sized holes near nostrils and/or gill plates and/or near eyes. Mabe
thin white threads trailing from these areas.

I read somewhere on the net that earthworms fed to the fish by itself
will cure it without a need to use medication...

Not just any earth worm, red earthworms have better nutrition - more
vitamin "D" from what I understand. As 'maria' pointed out, HITH is
most likely due to Hexamita, which could be due to poor water quality.
Treat with Metronidazole treated food - Tetra makes a medicated food
with Metronidazole, if you can find it. Otherwise see if your pet shop
has Hex-A-mit capsules. Their treatment is 1, 250mg capsule emptyed
into 10 gals. every other day for 5 days - repeat full treatment (if
necessary) in 3 days. It will be necessary unless you open one of the
capsules, mix it in a tablespoon of fish or shrimp oil and mix that
into 2 oz. of a good flake food, or into 1/4 lb. frozen brine shrimp
and feed twice a day for 10 days (or more).

I will also perform
50% water change twice a week until she cures herself & then go back to
my maintenance schedule of a 50% water change every other week...

Discus need *much* cleaned water than the rest of the fish on your
list. A 20% *weekly* water change leaves about 30 days of accumulated
DOC (dissolved organic compounds) pollutants in the tank. For the
discus, you need to do almost daily 20% water changes - they also could
use humic acids in their water, more so than the other 'soft water'
fish. I would put a piece of driftwood in the tank, or some peat moss
in the filter........... Frank