Hi and welcome.
First of all lets establish the volume of the tank. 3ft is a good length but it doesnt give hieght (very important later on for lighting) or depth from front to back.
For now though lets assume we are working on roughly 30 UK gallons.
This is a good size for a marine setup.
Now lets consider if you want fish only or full reef setup.
If you want fish only then lighting is not an issue as fish arent fussy
Reef setups need the correct lighting if they are to thrive. (more on this later)
Filtration. The best you can get is Liverock. Wether for fish only or reefs its simply the best you can get. The amount of live rock needed is about 1kg per gallon of water. (15kg for 30 gallons). The live rock will allow bacteria to grow on it and more importantly within it. Its the only filter that can turn nitrites to harmless nitrogen gas (algeas can do this too but really can only offer a supporting role to liverock).
Not only are you getting the best filter possible for your setup, its doubles up as great looking aquascapes! You will find the life that appears on live rock after a few weeks of being in the tank can sometimes be more suprising and interesting than the fish you have in the tank!
You can of course supliment this live rock with an external or internal filter. I would recomend this as its a great way to help with treaments etc. Carbon, Rowaphos and other items can be easily placed inside a filter this and be used effectively. Also the dark area within a filter like this makes a perfect home for amphipods and copopods (great food for the tank), they love to breed here in safety as the fish cannot eat them, this gives a steady supply of live food for your tank (not enough to sustain the fish but its a good additional vitimin suppliment)
Another reason for adding a filter like this is flow rates.
The ocean is not like a lake, its moves and flows (alot stronger than people realise). So its great to have extra circulation in the tank. A minimum of 10x volume turnover per hour in circulation is recomended for reef setups. (30 gallon would need minimum 300 galln per hour turnover)
Protien skimmer:
Many people say its an essential peice of equipment for a tank. I dont necessarily agree with this but it is higly desirable for the type of filtration i have recomended to you. If you want a fish only setup then i definately encourage one of these. If you want a reefsetup then i recomend a skimmer that is less effiicient (Red sea prizms spring to mind) A skimmer that underskims will allow "some" nutrients to return to th etank and help feed corals. An over effienct skimmer strips the tank of nearly all trace eliments and then you have to start adding them back for corals to live.
Lighting:
As already discussed, any light will sufice for fish.
if you want a reef then you have several options. The best get is Metal Halides. Expensive i know but they will be all you ever need for the corals in terms of lighting. They also make the tank sparkle which no other flourescent tube can do.
Most MH lights come in various powers. 150w, 250w and 400w. This is where the hieght of the tank is so important. If your tank is close to 2ft deep than i would say Halides are your only choice as you really need the power to punch down into the tank at this distance. Tubes are less powerful (but far more efficent) than halides. You will need to pack as many undr the hood as possible to keep corals. the hard corals like acropopra require very powerful lights!
You can now get T5 tubes that are much thinner than normal tubes. This will allow you to put more under the hood of your tank. Some people make the mistake that T5s are more powerful than standard T8s but this is not true. The center of the tube gives off the same amount of light as each other. However, by the time the light hace reached the outter galss ona T8 its lost power which makes it look less powerful. T5s tubes are thinner so they look brightrer only because they outter glass is closer to the center. As mentioned, the main advantage to T5s are that being thinner, you can fit more under the hood and thus get mor elight this way.
Hope this helps
