A sump or a fuge is basically tank that is in the cabinet underneath your main tank and contains all your hardware. For example: plumbing, wet/dry filter, heater, skimmer, live rock rubble, etc.
It sounds to me that you do not have a sump or a fuge which is fine since I don't have one either. You need a HOB
skimmer. The one that is most recommended on this board for a tank your size is the Aquac Remora Pro. You can look up its specs at proteinskimmer.com or captivereefs.com.
Live Rock is used for many things in a marine setup. The bacteria on the rock provides biological filtration which will work to maintain better water quality by dissolving the nitrites and ammonia in the water. Many forms of algae will grow on the LR
which can be used as a food source for some types of fish and inverts. LR
will also contain a lot of life on it other than bacteria. Hitchikers like shrimp, crabs, snails, brittle stars, and even corals can come on LR
. Not all of the life on LR
is great as mantis shrimp, some evil crabs, and aiptasia anemonies can come on the rock, but the good heavily outweigh the bad in lr
. I got my rock from my LFS
, but when I am ready to order some more rock I will order from liverocks.com since a lot of users from this forum have ordered from them and have been very impressed by the rock they have received from liverocks.com.
At least 1 lb LR
per gallon of water is recommended in a marine tank. This can get very expensive in a tank like yours so you might want to purchase a mix of dead base rock supplemented with enough LR
so that the base rock can be seeded with life from it.