hippo or blue tang

i have a hippo tang that i got about a week ago. i have read that they like to hide under rocks and stuff when you first get them. i was wondering if anyone could tell me how long that it will do this. i never get to see it and so far have never seen it eat. is there anything i need to be doing to fix the situation??

i have a 55 gallon tank, i first started it about 6 months ago. the only fish in it right now is the blue tang,2 percula clowns, 12 blue leg hermits, 10 turbo snails and 2 yellow tailed damsels that i bought near the end of cycling the tank. a freind told me the damsels were the best way to start because they were good strong fish. i have around 35 pounds of base rock and around 20 pounds of live rock in it. i have found that when i turn all the lights out, and wait to check on it for a couple of hours, the tang will be out but no more than an inch or so from his hole. i originally bought the blue and a yellow tang. the store i bought it from said it would be ok if i put them in together at the same time. but the yellow tang diedovernight. al water test said ok. i even took a sample back to the store to get tested and they said it was ok, but the stress level was a bit high. they told me it wasnt anything to worry about though. i put some seaweed salad in the tank for it but clowns seem to like it so i cant tell for sure if the tang is eating. i have read that they stuff theirselves under rocks when stressed but nothing seems out of place in the tank. i mean water seems good, fish getting along good.

he is only about 3 inches long.
i had done plenty of reading and already knew about the ich problem, as well as fin erosioa??? i think thats how you spell it.
the tang still looks good. nice color and still thick. he just wont come out from under,,, and i mean way under his rock. if for some reason i was to take out the rock for a day or 2, wouls this help him get used to the tank or would it just stress him out? any comments are welcomed. and i have found out that my lf knows absolutely nothing when it comes to salt water fish. i based alot of my setup off what they said. but after reading the threads here i might have to redo my whole tank.

thanks for the info. i guess ill jus twait and see if it gets any better. i have only ever seen 2 for sale at my lf, the one i got which was about 3 inches and they just got another. its about 1.5 and they were the same price. $46.

we have a place here that says they have the largest coral display in america. but as far as i can tell they have the largest prices in the world. i can easily buy2 individual fish from seperate online places and still get them cheaper than one at that particular place. well maybe not. but from the lf i have been going to a percula clown is only 15 bucks. but at the other they sell them for 50 bucks a pair. i even asked if they were mated pairs and they said no. they are just 2 fish nothing special. but on the positive side my blue tang is coming out just a bit. hiding in other spots.