Aquascape Pond Sludge Remover Packs eliminate pond sludge on rocks, gravel, and filteration. Sludge buildup is cause by fish waste, plant matter, and other decaying material. The easy-to-use water-soluble packs dose the sludge directly and make it easy to spot-treat and treat hard-to-reach areas. Pond Sludge Remover Packs are safe for fish, plants and animals.