Does your cube have an island style overflow so they can swim laps around and around?

It does so they can do laps if they want to. Overflow is right in the center and is 18" X 12".

my dream
 

that is a sweet sounding setup. something that I will definitely consider in the future when I get to build my own place one day.

That's awesome that they can do laps.

I think that negates any tank length issues.

No Ruth a 4 foot tank is too small for any tang let alone the Powder Blue and Achilles. There is insufficinet length to meet the needs of these two.

You also need to know that the Powder Blue is a very difficult tang to keep. They are ich magnets, prone to disease and oftern perish after a few months taking there tankmates with them.
The achilles is an almost impossible tang to keep. Those very few who have success have large mature tanks. Pristine, highly oxygenated water is essential.
Ruth, as you know tangs are swimmers. Sorry but a four footer doesn't meet the requirements.

I think a 4 foot cube would be enough swimming room for any tang.

I look at it as, how much can they swim without having to stop and turn around? In the 4ft cube, is is never, they can swim 16ft before doing one lap. In a 6 ft tank, it is just 6 feet because of rockwork and corals.

Sure they have to turn a bit, but what fish on a reef dont turn all the time? They dont swim perfectly straight. If a 6ft tank is good enough, I would say a 4ft cube is more than large enough.

Thanks for the replys. I am aware that both Powder Blue and Achilles are challenging to keep and would not even try it in a smaller system. They would definately be the last fish I added and even then only after the system had been set up and stable for at least 6-8 months. I don't think that well oxygenated water will be an issue as I plan on having 4X6200 tunze streams as well as a Bubble King 500 skimmer. I do regular water changes on all my tanks of at least 10-15% a minimum of every 2 weeks and other that the 190g that I am running zeovit on do not add a bunch of "stuff" to my systems.
I am still undecided but just looking to collect as much information as I can so really appreciate when people take the time to pass on their knowledge.

U go Ruth the main thing is that the tangs are cared for at the top quality. I have 4 tangs in my 170 60x27x24 and they are small but they swim around until i get up the nerve to build my 8 footer soon i hope...

mike

Great Ruth.
You already have a large tank so you are aware of their swimming needs.
There is some great info on tang requirements at www.wetwebmedia.com

Well it appears at least to me that tangs in general are more of a naesco
magnet then ich. :p