There are actually a lot of fish that rest on the bottom of the tank when they sleep...clown loaches will even lay on there sides, which freaks people out when they first see it ..they think they are dead! As far as the gravel goes, just scoop some out with a plastic cup or the like. I like using a Python water changer, especially with a lot of tanks to keep up! 20% every other week at least is a general rule of thumb...do more if you have alot of fish, or grow out tanks, etc. I personally do at least 50% every week, but I have a lot of stock and breeder tanks...Good luck to you Hilldaddy, and feel free to ask any questions...there is a wealth of information on Aquaria Central and a lot of good folks that are willing to help! Take care!