This is our 3rd summer with a 15'X48" Intex, we upgraded to a sand filter this year. SO much easier and will be less cost than a seasons worth of Intex cartridges. We didn't learn about Unicell and Filbur replacements until after the sand filter was ordered, so I can't comment about the cost and effectiveness of those. Intex cartridges DO let LOTS of "stuff" bypass.

This is the setup we have
http://www.intexcorp.com/index.php/h...s/56673eg.html
It is larger than we need for our 15' pool but should work very nicely for your 18'.

If your pool came with the 1-1/2" screw connection hoses and plunger valves, it is a fairly straight forward change over. If you have the 1-1/4" clamp on hoses, it is a little more involved.

Here's a link to our change over thread.
http://www.poolforum.com/pf2/showthr...041#post117041

There are several SWCG options here
http://www.intexcorp.com/index.php/h...er-system.html
I'll tell you upfront that the ozone generator is not generally recommended (at least on this forun) for outdoor pools, so don't waste the extra money on that. Also, I'm pretty sure that ALL Intex SWCGs include a copper ionizer, and you "PROBABLY" will want to disconnect it, unless you like turning blonde hair green and stains on your liner.

Good Luck and ENJOY your new pool!

Pappy