Considering an Aggressive tank setup or some type of large fishes

[andrewjardin]

I have a 112 Gallon aquarium which I have been planning to set up as a reef tank, but all things considered I enjoy my current little 30 Gallon reef tank, and could just throw money into making it better rather then upgrading to the 112. And in turn I could set something up and have just a fish only tank, like maybe a grouper, or something unique usually not considered reef safe. Is this tank too small for any kind of shark?
Layout of what the tank will look like once its set up as saltwater.

 

[andrewjardin]

Actually i think what i want to do is have an eel in here. They are definantly cool creatures! And my dads buddy's friend is selling his 75 square tank and all pumps light everything including an eel and two larger fish for 100$ so i definantly am trying to get ahold of him so that i can get that awesome deal! Im not sure of the species in his tank, so im planning to find out sometime next week when my dad is working with him again.