I'm guessing you mean Pseudanthias tuka and not Pseudanthias pascalus.
Your tank size is fine.
Depending on where and how deep they were collected ( those collected at deeper depths may never adapt to our higher light reef tanks ). They tend do best in a school of 5 or 6 ( though 1 in a tank is fine and many authors suggest keeping just one ) so either purchase all females and one will become dominant and turn to a male or purchase a male and a harem of females.
They need medium to strong current and plenty of hiding space in the upper layers of your rock.
These do not usally adapt well to other foods such as flake, bits of shrimp, mussels, squid, frozen preparations, etc. ( their mouths are small and their metabolism is fast ), so they should be fed at least 3 times a day live or frozen enriched brineshrimp ( Selco/Selcon is great for this ) and frozen daphnia released into the flow.
Regards,
David Mohr
[ July 27, 2001: Message edited by: davidmohr ]