Originally Posted by Pasfur
Reading this entire thread again, things seem to be moving rather normal for you. You have a pretty good setup, with 100 pounds of live rock and an ok protein skimmer. What has helped at this point is your stocking levels, which are small enough for the protein skimmer to do an effective job.
I am very concerned about the future of your tank, because a Yellow Tang is a rather poor choice of fish for a 55 gallon tank. This species is extremely territorial and makes life difficult on almost all new fish additions. This behavior is greatly magnified in aquariums under 6 feet in length. You will need to be extremely cautious with your future fish additions, and stick with fish that are not in any way perceived as a threat by the Tang.
But Provided that you can accomodate larger quarter in near future, you can start with qurter or even half dollar size yellow tang(s) if you really desire.
Even in 6' tank, any tang who already claimed this tank as its KINGDOM, it would be a challenge to add just another tang.
Adding of new tangs in a tank which already has the BOSS can be done but required few strageties by keepers.