Check the listing for details. Pond Bacteria Sludge Remover Blocks. Condition: New. Listed at 319.49 USD. Pond Bacteria Sludge Remover BlocksSludge Remover Bacteria blocks are designed to remove organic sludge from the bottom of lakes and ponds. Sludge is the result of fish waste, dead algae or plant material, uneaten fish food, leaves and other debris. When introduced to the water, the blocks sink, dissolve and begin to remove bottom organic sludge — often several inches per year. Sludge Remover Blocks are great for spot treating around docks, beaches or partially treating large ponds. Reduce sludge buildupEliminate pond odors caused by stagnant water and decaying materialImprove water clarityReduce oxygen demandReduces problem causing nitrate and phosphatesEnhance water clarity and reduce murky waterHave results in temperatures as low as 38°F with cold water bacteria strainsSafe for fish, family and pets