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 doesnt 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.