I know everyone on here talks about deep sand beds and not bothering them, but I use an agronite that is just big enough that I can suck a lot of the crap....literally out to the sand bed with the syphen. I use a fish net set into a bowl in the sink to catch the baby brissle worms that I suck out. It keeps them in the water in the net in the bowel until I am done cleaning, then I put them back into the tank with the net. All of the sludge form the agronite goes through the net, but not most of the worms. I think that this is the best way to remove nitrates, but I could be wrong. I don't know how long a deep sand bed takes to become anearobic after disturbing it, but mine is only a couple of inches....I could not stand it if I had sand that was to fine to vaccuum out the crud. It really bothers me to just leave the fish waste there to rot away. I like to remove the cause of the nitrate directly. In my mind I can't see how just removing water and not the debris at the bottom could help much. That is just my thought on the matter. I really don't know the real answer, but it works for me. Lesley