I forgot to mention it but you shouldn't gravel vac every water change. You wont be pulling out much if you do it frequently.I like to do or every 6 months. It's a pita so doing it every few months is best. Raking the sand is good only if your running a filter sock to absorb what's being released, otherwise it will just settle somewhere else. Also only rake a little at a time because what's being released will stress out the livestock. With a gravel vac nothing gets stressed out because the dirty junk is going straight into the siphon Hose and thrown away vs being releases into the tank.