From what you've posted it doesn't look to be either a lighting, or nutrient issue. 8 T5 bulbs are a ton of light over a 75 no matter what the bulb combination, you could grow SPS at the top of your tank with half that many bulbs.

If your test results are showing 0 for nitrates and phosphates, and you have no nuisance algae, likely high nutrients aren't the issue. Also if you're pulling out skimmate you likely have enough nutrient to grow corals.

Probably it's something you haven't posted yet.

What is your water change regimen? (did I miss this)
Any corals in your tank known for chemical warfare? (leathers?)

Are you corals brown or more of a faded tan color? Brown is caused by high nutrients/low light. Corals tend to go tan and loose color when they are stressed, such as by contaminates in the water, unstable parameters, etc.

One thing I've thought of is the possibility of chemicals being excreted, or trace elements being used up by a large mass of macro-algae in a small system.

Just my $0.02 Rob

I think you also have to accept that some corals just simply shock easily from having been established and was used to one system (aquarium), and then all of a sudden being shoved into a new one. It can take them a very very long time to regain their former glory. Some may never achieve this and some will colour morph into something different. It is not necessarily a matter of bad parameters, but rather different parameters and conditions from what they previous were used to. Take your red coral turning pinkish for example. It is virtually impossible to reproduce ALL the parameters and conditions of their previous tank. Some corals can adapt quickly and easily, some (or perhaps most) do not.

I have a coral right now that was once red, then browned a little, now has coloured up with half of it being blue!

my 2 cents.

K.

I'm actually intrigued by the stray voltage idea. I did a quick test using my multimeter and it looks like I have 0.6 to 0.7 volts running through the tank. I tried the same test with my pico and read 0 volts. The zoas I moved from the 75 gallon to the pico perked up very quickly. So would 0.7 volts be enough to cause a problem?

Its pretty much just the sps and zoas suffering. The LPS and other soft corals seem to be doing well. The maze brain has about doubled in size in the last few 4 or 5 months. The pulsing xenia are growing and pulsing. Chalices are growing slowly, cyphastrea is growing. So the puzzlement is in what could be causing problems for zoas and SPS but not so much for the other inverts and fish.

It does seem to be more that the corals are losing colour and going tan rather then dark brown. Water changes are about 9 to 10 gallons every week to 10 days. I do have two small leathers so I don't know if that could also be a problem in the larger tank. If so they could go. I'll try to post pictures and dig up my last test results later on.

I think this might be part of your problem. I just had a problem with the alk in one of my tanks and all my corals turned brown. They are coming back but it is taking some time.
I do think your fish load could be a problem. When I was running my other tank with fish I had great color then when I transfered just my fish over to my other tank my corals slowly faded in color they did not turn brown but the color faded out over a few weeks. I was not feeding at all at that time as there were no fish.

It would be cool if it was that simple! I'm curios to know where the voltage leak is.

Looks like 0.4 to 0.5 volts from the heater and maybe 0.2 volts from my return pump. The pump could be putting out some inductive voltage due to the proximity of the motor to water. The heater is obviously leaking current somewhere. Looks like I'm picking up a new heater tomorrow and maybe a grounding probe for the sump too.

As for test results, on Nov 8th I had this:

pH 8.4
PO4, NH4, NO3, NO2 all zero
KH 7

Here's some pics of the corals. This first one was brown when i received it. it has since turned a lighter brown with a touch of purple on the tips but that is as good as it has become.
http://hotimg23.fotki.com/a/70_70/254_23/Coral1.jpg

This one used to be a nice right green but has since become more of a duller yellowy green.
http://hotimg23.fotki.com/a/70_70/254_23/Coral2.jpg

This frag is about twice as big as when i received it. The tips have turned a bit pink but the rest has stayed beige.
http://hotimg23.fotki.com/a/70_70/254_23/Coral3.jpg

here is the previously red mill that is now more peach coloured.
http://hotimg25.fotki.com/a/70_70/254_23/Coral4.jpg

A previously nice green slimer with blue tips that is now going completely brown.
http://hotimg23.fotki.com/a/70_70/254_23/Coral5.jpg

This frag has grown somewhat from when I received it but colour has not changed at all in the last 5 or 6 months. The tips are a nice green but the rest is brown.
http://hotimg25.fotki.com/a/70_70/254_23/Coral6.jpg

This one has just faded from where it was white with blue tips. The blue is much more faded now.
http://hotimg23.fotki.com/a/70_70/254_23/Coral7.jpg

Another thing to note is polyp extension has not been as good as it used to be either.

So I hope the stray voltage is the answer. Will see how things do once I address that.

Pics look like what I am going through. i still think its your Alk I can post some of my pictures but they are the same as yours more or less.
7 is a bit low for Alk I am trying to bring mine up from that as well but my PH is at 8.5 so trying to bump it slowly.

FWIW my parameters
PH 8.5
Alk 7.6
Mag 1350
Ca 420
Strontium 6-12 Hard to read
PO4 0
No3 0.2
My LPS and clams are looking great its just my SPS and they are coming back slowly after the Alk drop.

I went through the same thing I never could get the realy nice colors so I switched over toa full zeovit system and in 6 weeks my tank has chaned so so so much.Every one of my corals got color to them that I didn't even now they had. Imo amino acids without full zeovit gave me a huge alge bloom.