120g will be fine for a good while if you are getting from an egg, but I think a 180 is even to small for a bamboo, as when it approaches 2 to 3 feet in length, itll have trouble turning around, that is why I would recommend a square tank (whoses sides are greater than the sharks length) or a tub to anyone who gets a shark. If you plan to breed, nothing less than a 400 gallon tub.
First, What else is in your tank? If there is nothing, It will fine, If you have other fish in there, do some research and check if they are compatable, because some people have problems w/ shark/fish combos. Just research research research compatabilities is all I can say.
Food:
At a younge age, You could try feeding it lil pieces of krill or silverside, but if its not accepting those, or having trouble eating them, your best bet would be to put a cube of mysis by it, it should be easier for it to digest the mysis, and from my experience, its your best bet to intise it to eat larger food early on.
Lighting:
Depending on how you want your tank to look, and what you have in it, can change your lighting preferences. Stuff like MH and T5s can be used, but they need to be positioned high above the tank (at least 12inches +, I run my MH at 22 inches). If the lighting is to intense for the shark, they shark will react adversly, If its only a shark tank, the less lighting you use the better, running a simple flouresent and some moonlighting would work perfectly fine. Remember, Bamboos are, for the most part, Nocturnal.
temp.
Again, this really depends on your shark, Most sharks like colder temperatures, The range from 72 degrees to 78 degrees should be fine. My shark seems to prefer it at 80 degrees, so, I would advice you do it in the 72 to 78 range as that is usually the norm for them, and what I have seen most people running.
Behavior:
Bamboos, for the most part, are nocturnal. Expect to see your shark hiding or hugging a wall of the tank while your lights are on. They are also bottom dwellers, so dont expect them to be swimming lots and lot through your tank, they will pretty much live on the bottom of your tank, and kinda hover around at night between structures.
Rock:
Do not add alot, but, add a large enough structure for it to hide, most or all of its body behind. If you do not care too much about appearence, you could just use 1/2 of a large diameter pvc pipe. If your shark doesnt like its structure, itll be sure to tell you my either knocking it down, or moving it around
. Make sure your substarte is sugarsized, as anything larger might cause the shark to get irritation upon its belly.
Id recommend HEAVY filtration, as sharks can be messy when they eat, and even more messy when it comes out the other end
. You will need a protein skimmer. Id definetatly recommoned a wetdry, not only to put ur skimmer in, but to pick up alot of the excess pieces of food the shark doesnt eat, I seem to be constantly picking lil chunks of krill and silveriside outa my wetdry every few days
just remember, the 120 will work for a tank for while, but it wont last forever, You will eventually need to upgrade or get rid of the shark when it gets to large. Id recommoned you ask your LFS you are gettin the shark from if they would buy the shark back if it gets to large, Just in case when the time comes to upgrade, and you cant afford, or have trouble getting it together.
Hope that helps