wait it out. 450 gallons is a big setup - I can only imagine the amount of sand you are using.
Cleaning sand is easy but tedious - especially in large volumes.
heres the run down;
http://www.reefaddicts.com/content.p...an-Old-Sandbed
Pretty much you need a bunch of buckets, lots of time, a garden hose and patience.
I dunno what you paid for your sand but be ready to waste an entire weekend doing it if not more (still cant wrap my mind around how much sand you will need to move/clean, lol)