Over time a layer of sludge builds up on the bottom of most ponds. Sludge Answer is a blend of beneficial bacteria used to remove sludge from the pond and filter system creating a cleaner pond and a better environment for fish to enjoy. Use Cloverleaf Sludge Answer frequently in established ponds to keep levels healthy. 1 litres will treat ponds up to 5000 litres (30ml treats 150 litres).