yep tracy got it!!! i know alot of people use urchins in their big tanks for this.
lennon as for my water changes i mix up a large amount of saltwater in a container and store it away. this way whenever i want to change some water i have it right there ready to go. and when i do use a water change i change less then half a gal or so.
as for a filter, i have a hang on the back type that i got from walmart. its one of the smaller ones i think. this works well for me, however i would like more water flow in the tank, other then that it is a very balanced system.