Co2 Diffuser

[ChrissyBoy]

I've decided to buy a CO2 diffuser to give my plants a bit of a boost. However, I've never used one before and have no idea exactly what I need. I have a fairly heavily planted tank with many varieties of plants/mosses.

My dimensions are 4ft x 2ft x 1ft, 224L, I have black volcanic glass gravel and a 36inch powerglo bulb.

Can anyone help me out with this as I'm going to ask for all the stuff for xmas.

Thanks!!