I have had the achilles in my tank for a while now. He's happy with my other 2 tangs (yellow & hippo). I came across a good deal on the Purple tang and would like to add it to my tank. I read somewhere that the Achilles should be the last tang added. So now if I want to add the Purple, would I need to take out the Achilles then add him back later? How long before he can go back in?