Johny

Bigger the better.

I run an eheim 2260 on my 6x2x2 and it keeps my water crystal clear. They fit the most amount of media than any other cannister on the market.

Pricey but if you were to run a single cannister on that size tank this would be my pick.

Check out the Aquafresh NemoLight series. Aquotix/Vebas/morley aquariums sell them. Youre able to adjust the settings for different applications like make it dimmer, make it brighter, even the colour affects like adding more blue/red LEDS or having none at all.

Highly reccommended. 4FT version does my 6x2 more than adequately. 

Plenty at the moment - 

City barn malaga, pet magic, robs aquariums and I think Morley aquariums all have at least one that I know of.

With the eheim classic there is no auto prime either but surprisingly primes so easily.
Update - tank is now filled and been running for the last few days with water. Of course of all things I forgot to get was an air stone so still need to sort that out haha.

Here is how she is currently looking with rocks and driftwood in - 

Close up of the Garnet - 

Wish I could at this stage haha she should sell soon though its a steal! Then you can consider giving up those birchirs