with displacement from live rock you have less than 270 litres - estimate it out at round 1 litre of water for every lb in weight of rock. Then, what other fish do you have (adult size)?
Seffie x
ps 75 gallons for the smaller yellow tang (obviously all according what else you have in the tank) - just been and checked, you have less than 60 gallons (without displacement) so sorry to say, your tank is not really suitable for Tangs
Tangs are so prone to diseases like ich, that keeping them in smaller tanks just tends to make an already problem, worse. Your tank isn't an absolute horrid size for a tang, but i'd defiantly think twice about it. If nothing else, I think a kole tang might be OK