Toxins build up in the sandbed and are released when you vacuum thats why you only do small sections at a time over days or weeks or in that guy's case a year... You do not want those toxins being released into your water column....remember STABILITY is the key to a reef and when you vacuum the sandbed it THREATENS STABILITY so you do it very slowly and over days or weeks ...dont be a rockstar and see how fast you can clean your sandbed or you could be very, very sorry....there is more that could go wrong then the right.....just my two cents and opinions may vary thasok.