Tang fight

[Chin_Lee]

Ruth
the naso is probably enjoying being the king of the tank right now. They are also quite territorial and considering his size, hes not going to have much tolerance for other fishes that may challenge his authority. If you had several other medium/large fish in there with the naso already, i would consider but with your situation, any new tangs are going to get some whoop-ass.
if you are going to add one, i would take the following precautions and steps:
1) put your new achilles into a QT tank and take real good care of him for 2-4 months. Its almost a guarantee that they will go through a long phase of ICK that you will need to help it get through until his immune system kicks in to "captive mode" level. Feed religiously of mysis, nori, with selcon and garlic. When you see the new tang free from ick and gaining weight, let it get plump to store up energy reserves.
2) transfer the fish to a sump of your display tank. This will get the fish used to the conditions of your display tank. And if it gets stressed and ick out again, then you can try to pull him through while in the sump or if it gets really bad, at least you can catch it again and QT tank phase again.
2) get eggcrate and create an area in your display tank that you can introduce your new fish. don't make it too small or the confined space may trigger stress and another ick attack. so you will have to basically create a barrier in your tank and will look rather ugly for a while. I would recommend at least a 2x2 area. then when your tang is healthy again, put him into the isloated chamber of your tank. This will ensure the naso and achilles can see each other but not allow any direct attacks from the naso.
then you will just have to play it by ear. if the naso sees the achilles and does not give a hoot, it may mean that the naso is not threatened at all by the size difference (although unlikely unfortunately). if aggresssion is observed (which is the more likely scenario), monitor and assess. After a few weeks, the naso may eventually "believe" that the achilles is immune to his aggression and there is no longer a need to be as aggressive. After a week or so, continue to feed but make sure your food gets squited into the same area of the egg crate where both fish will have to eat with the other one close by. when they can both eat while being close to each other, you may be on the path of acceptance. But the presence of the naso and its intimidating size may trigger the achilles yet into another ick outbreak.
in general, i would consider the risk pretty high of losing the achilles to diseases by itself. The naso tang factor will make its survival probablity even worse and may be the last factor that deals the final blow.
I have an achilles that I've been babying for the past 3-4 months in my sump and i put him there so I can monitor his ick outbreaks and feed him directly (tang police - please note that the sump area that it is in is a 3x2 of free swimming space).i bought him from another reefer who had it in captivity for 4-6 months prior so hes coming up to a year in captivity and i have a real good feeling about his survival rate at this point. hes pretty much ready for a display tank but i'm in the process of planning some major overhauls on my system so he will stay in there until i can sort things out. But i won't introduce him into my display with the purple and yellow just because I don't want him stressed. If he goes into the display, the achilles will be the only tang in there.
PS - did i mention how susceptible achilles are to ick???