ok so first off: the biocube 29 tank is an awesome starter tank to get into saltwater. First, take out all those bio balls/stars and replace them with small pieces of live rock. (if you have to buy rock such as picanny and break it so you have small pieces to work with) The liverock will work much better than the bio balls will.
Second, the lighting that the cube comes with is pretty damn good. Its made to do corals in it. Honestly, since its only 29 gallons, you really HAVE to do coral, otherwise your gonna get bored with it. Since you cant put too many fish in a tank of that size.
Get the live sand/ rock and set up the tank. Id start off with some cheap damsels at first, to help cycle. Once your water is good id recoment fish like an ocelleris clown or two, as these are not too expensive and dont get very big. Plus they are one of the few clowns who enjoy being with more than one. As far as other fish options, do a scooter blenny to help clean your sand. You should defently buy an angel of sorts for your tank. But you can only have 1, as more than one will fight. Id personally go with a flame angel, or a coral beauty, but there are a few more out there as well.
O and also, once your tank has cycled, before you put any coral or other fish in the tank id do my best to take out the damsels. They can be agressive towards the other fish you might put in the tank, and i just think there kinda lame. Trust me, take them out before the corals go in. Your gonna have a tough time catching them later on if you choose you dont want them or their killing your fish.
another cool fish that i would get is a mandarin goby. although you dont wanna get one till your tank has been running for about 6 months or so, for they are extremely hard to get eating frozen and flake sorta foods. They will eat little bugs/ creatures that your tank occur in your tank naturally through the rock and such. Once you start getting algae on your tank i would buy a sea hare. Problem is some do such a good job that they clean all the algae and then die off cause lack of food.
hope that helped you out a bit. I work at a fish store, and get asked millions of times each day "what can i get in a biocube 29 gallon" so its kinda been second nature to me. Although i do not personally have one, i jus thave to take care of the few we have set up in our store.
