So, to keep this thread on track and going off of your what I can only guess is your now current tank you mentioned in another thread (60cm x 45 cm x 45cm).
I would personally skip on the tang.... yes tangs "can" be kept in smaller tanks for a temporary time. But a blue tang of any genus will outgrow that tank in less than a year. Rehoming large fish can be a huge problem in the long run, especially if your not in or near a large city with a large salt water presence where you can find a new home for them easily (And these homes will not be in endless supply).
It may sound like some are being harsh, but we are looking at the long term ramifications of housing a large fish in a smaller system. Your tang will be much more susceptible to illness being in a smaller tank and stressed out which could wipe out your entire tank quickly. We are offering advice (which is what you came for) and it may not be exactly what you want to hear but you need to hear it...
We all want the best, for you and your fishy friends and are just trying to prevent a difficult and stressful time for you.
And trust me, my BRAND new tank is only 5' long and I do plan on having one or two tangs. But even I don't want to put myself through the struggles of having to rehome a fish so even I'm skipping some of the tangs I REALLLY want because I know I can't provide them with the proper home long term. We grow attached to them over time and it becomes more and more difficult to send them away to a bigger tank somewhere else. You have plenty of fishy friends in your current tank, enjoy them, and plan ahead to build them a larger home down the road where they can share it with a blue tang in peace.