Unsuccessful Blue / Yellow Tang Keeper

[Gooi]

I have started a 2 feet Reef since December last year. It has been nine months already. Have purchased 2 Yellow Tang and 2 Blue Tang. Unfortunately none of them can last longer than 2 months. Really don't know what is going on. All of them came in healthy for at least 3 weeks and have no problem eating. But 1 week before they die, they will lost their appetite. BTW, all of them also have white spot (Like Parasite) starting the first week and gradually heal after that but some will get it back. Really do not know what is the deficiency behind that is preventing my tang to adapt?? Help is needed.
The fish that still around are Tomini Tang, Maroon Clown, Domino Damsel and Blue Damsel. All these 4 fishes are around since December and seems to be healthy without any parasite attack.
Beside fish, I also have the following coral. Rycodia, Open Brain, Tooth Brain, Trumpet, Cauliflower Colt Finger, Acanthatrea, Clam, Disc Anemone

 

[pvn228]

You have too many fish for a 2ft reef.

But yeah you have ich parasite and i dont suggest you get another tang unless you can supply them with at least 75+ gallons of space. tangs are susceptible to ich parasite. your other fishes hav prob built an immunity against it. if not they will die soon also. (i had the same problem)

tangs get very big and needs plenty of space to swim.

 

[WRASSER]

Gooi,

what is the temp of the tank?