I put a sand filter on mine just about two weeks ago. It took a little imagination to plumb it between my Intex pump and SWG, but it works and its AWESOME!! I used a 200# filter from ebay for $230 free ship. Its blue with a white valve assemly on top if you go looking for it. My pool was NEVER so clear as it is now. As an added benefit, I left the Intex filter assembly intact, so if I wanna use cartridges, its still there. I can put the sand filter on recirculate, and drop a cartridge back in the Intex canister, and poof, back to cartridge. Not that I would ever want to. With sand, plumbing, and backwash hose, total cost was right at $300. And that's a filter rated at 3300GPH, and 21k gallons. Seems to be the perfect amount of overkill. About 35%. I can send pics of my setup and plumbing if you want to see how I did it.

I'm workin on lighting now.... :-)