I don't know anything about the sizing of SWCGs, but you might want to look through this thread to see if this helps any...
http://www.poolforum.com/pf2/showthr...sizing-of-unit

Also, I don't know about about possible corrosion issues on the AG pool--I know that adding SWCG to most AG pools will void the warranty, but I don't know if this is an issue for you or not. Just something to think about.