Interpet Sludge Buster is suitable for use in cold-water and tropical freshwater systems. Solid organic waste accumulates in the aquarium and blocks up filters. It comes from fish excretion, excess food and dead plants. This sludge is unsightly and unhealthy, encouraging disease causing bacteria. Sludge Buster is a culture of safe bacteria, which speed up the breakdown of solid organic waste. When to use sludge buster. -When you want to improve the appearance of the aquarium. -To reduce the levels of disease causing bacteria. -To reduce aquarium and filter cleaning. -Use every 2 weeks to ensure optimum sludge breakdown.