Small SW tank filter?

Live Rubbel, PH Removers, Carbs

I'd go with an Aquaclear 5-20. Place some live rock rubble on the bottom, then use the filter pad that comes with it and cut it if needed. Biological and mechanical filtration, all in one! It also comes with media. If you can fit it in there (they leave a lot of room, bless their hearts!) then put it in. If not, hey, you got a free bag of media to put in another filter.

Oh, and live rock doesn't mean you need coral. Live rock is basically the end-all, be-all of biological media. You know how in freshwater fishkeeping we have to do water changes, because we don't have bacteria to convert nitrate? Live rock does it! My SW has no nitrate. I mean, you still need to do water changes, to remove dissolved waste, but it's amazing (to me, at least, a mostly-FW fishkeeper). So little bit of live rock goes a long way, and you don't have to have coral. Live rock is really beautiful on its own -- the purple coralline algae, the little critters that come out, etc. But, if you don't choose to have it in your display, you can always ask for the little pieces and put it in the AC filter. My LFS gave us a bunch for free for our sump.

i prefer live rock in the tank and nothing in the filter. filters always get clogged and its a pain cleaning it out all the time.

in marine tanks usually filtration is done with live rock, the live rock has the bacteria on it that converts the nitrogen products, a filter could be useful for running carbon or other such chemical media. you could also use it to grow a mangrove or macro algaes which will reduce your nutrient levels.