sick emperor angel, I have no idea what it is!

[Delphinus]

I immediately suspect skin and gill flukes. Angels in particular are very susceptible to them and the more I am learning about them myself, the more I am realizing how prevalent they are in many systems, private tanks, LFS and distributor tanks. Odds are VERY good you have them.

Faded colour, hazy or spotted eyes, and frayed fins are 3 of the classic symptoms. There are other symptoms as well but they do not have to display all symptoms.

The good news is it is treatable if caught early enough, and the medication is safe enough for use in a reef tank, although it will be hard on your tank, things will pull through.

Here is some additional reading for you:
http://www.canreef.com/vbulletin/sho...ighlight=fluke

This thread has been a real eye opener for me.
http://reefcentral.com/forums/showthread.php?t=1260067&
I'll summarize some key points:

The obvious symptoms:

1) Fish twitching the head side to side once in a while like if wanted to shake something off his head.

2) Discolored blotches of skin (Most people think this is velvet or some bacterial infection and misdiagnose it with antibiotics)

3) Frayed fins or tail.

4) Sudden loss of appetite. Fish was fine yesterday but today it's not eating at all.

5) Cloudy eye(s)

6) Rapid breathing

The treatment is with a pharmaceutical called praziquantal. You can get it as a powdered form in the bulk as Praziquantel, or in hobbyist packaging in the product name "Praz-tastic" (both made by National Fish Pharmaceuticals, more info here: http://www.fishyfarmacy.com/products4.html {scroll down to about 1/2 way}) .. or in liquid form "Prazipro" (made by Hikari, more info here: http://uskoi.com/prazipro.htm ). If you can't find any locally, check with pond suppliers as it is commonly used to treat flukes on koi as well.

Flukes are a flatworm. You do need to act on this as once they move into the gills of a fish the fish will stop eating and death can become imminent.

You can try a FW dip in the meantime (match temperature and pH, some good tips for "how to" in that reefcentral link I posted above), the flukes will fall off and will be visible to the human eye ... however bear in mind that this is only a temporary measure as it will not get any free floating flukes in the tank, fluke eggs, or flukes that have spread to other hosts (ie., your other fish).

If you use the powdered form (it is stronger), you first have to dissolve it in vodka as it is insoluble in water. This makes it harder to use but it is a stronger dose. Prazipro on the other hand may be weaker but it is already in liquid form so easier to use.

In a bad infestation you will have to do more than one treatment one week apart.

Good luck. As you can tell from the first link I posted I have recently went through this myself. The good news is that after treatment my fish are recovering, so I can attest to the effectiveness. I decided to treat my whole tank as it had escalated quite badly before I realized what had happened and all my fish were at risk.