I agree 100% with Anemoneman, but I'd like to add a small clarification.
When Yellow Tangs shoal they usually swim 2 or 3 feet apart. That is like their "personal space".
A tank able to house 6 Tangs with 4 - 9 square feet of "personal Space" for each fish would need to be at least a 700 gal
, preferably 1000 gallons.
It's your tank and 6 tangs will fit in a 100 gal
, but I would not expect them to live very long.