Its natural, but its not nice - were talking about sludge of course.  This build-up of excretion, left-over food and dead plants creates an ugly sludge blocking up your filter media, and is a breeding ground for disease-causing bacteria.  But it doesn't have to be like this.  Sludge Buster helps reduce the build-up of sludge in your aquarium.  It contains a pure culture of safe essential bacteria to tackle sludge head-on.  These bacteria act like an army of workers breaking down the sludge and clearing your aquarium, turning it back into a clean and healthy environment for your aquarium community.