Help, tank yucked up.... urgh!

Hello everyone!

I have an 11-month old tank that was doing very well up through early
August when I had to go off on a 90-day trip to the middle east. Well,
I'm back now and my oldest son, who was feeding and cleaning the tank,
"forgot" to empty the skimmer the whole time I was gone! So, this
morning I came in to find a nice nasty skimmer covered in dried green
goo that doesn't seem to be doing anything and a tank that's covered in
1/2" of solid growth on the walls and rock.

Best I can tell I've lost all my corals, shrimp, most of my snails (I
have three very large conch now), and have maybe 3-4 crabs left out of
an original 20. I've lost both yellow tangs and my pseudochromis. The
two clown fish seem to be doing well, although the anemonie is missing.
There are also two crocea clams in the tank which (strangely) seem to be
doing well as they're both large, open and reactive to light.

I've cleaned the skimmer completely and it has produced two full cups of
skimmate (very wet tea - I'll dial down the air supply later) so far
today. I also scrapped the walls of the tank and then used a net to pull
the floating debris out of the tank. I've cleaned the filters for the
wave maker as well as the prefilter for the sump and swapped out the old
chemi-pure bags in the sump for 2 new ones (after rinsing).

Anything else I can do? Much of the growth on my 150# of live rock seems
to be some kind of slime mold - maybe red slime algea? It's already
everywhere in the tank, so is there a fast way to remove this? And the
same growth is all over the sand as well.

Any help or pointers would be appreciated...

tia,

mark h