forgot to mention, if you can spend the extra £££ (and its not too much) you might want to consider this
http://www.seachem.com/products/prod...s/Purigen.html
i have started using it and so far seems promising (peeps on forums swear by it, but i am reserving judgement)
telboy has a good point about filter wool, but i have found this to have its own pro's and con's whereby others have had nothing but good feedback about it