what is wrong with my tank?

[sweettooth162]

i have 4 blue tangs in a 400 gallon tank. they are also with some perc clowns 2 damsels and some chromis. all of the tangs have some sort of thing that is making them loose there facial gils.this is also being experienced by the 4 striped damsels. they also have ich which i am working on. but does anyone know what this might be? plus there is alot of brown algea it is covering all of my corals and the substrate (crused coral) it is even growing on the glass. the tank has been running for aprox a year with little problems but now everything seems to be out of control. but all my readings amonia, nitrate, nitrite are normal any clues?

 

[jacrmill]

sounds like HLLE (head and lateral line erosion or something like that) to me. but ive never seen it, ive just read a little bit on this board and know tangs are very suseptible to it. might wanna put this in the disease and treatment forum. theyll know alot better than i.