2.5 pico tank / Noobie question

I would highly recommend getting a 15g or 20g tank if your interested in getting into saltwater tanks. Starting out with a pico set-up would be a steep learning curve. Plus setting up a 20g would be roughly the same price to set-up anyway.

With a 15g or 20g you could just get some sand, a powerhead, a light (a double T5HO would be perfect) a heater and some live rock (however much you want). Just set everything up, get you water testing down (sg, KH, calcium, ph, ammonia etc), add your live rock and wait for the cycle to be finished. I've left out the details but that's the basic idea of how to set-up a marine tank. With this set-up you could have a couple of fish, inverts and a choice in corals.

With the pico you would be limited to a few corals and maybe some inverts. The sump idea plus a canister filter would be good for increasing the water volume (and stability) but still I would go with a bigger tank, its easier.

i agree, your never content with a small SW tank, my first was 8 gallons and its was torture because i wanted all sorts of big colorful fish that i couldnt get

YES! Cam191919 is right, that is exactly what will happen, you will just end up getting a larger tank anyways, why not cut out the middle man? The larger volume will be far more forgiving on you as well, do as TropicalNorth Suggested get a 20g,it will save you allot of trouble.