Velda Pond Sludge Destroyer Bio Oxydator - Eliminates Pond Sludge and Adds Oxygen. This easy to use Velda pond treatment removes sludge from the bottom of your pond. Fallen leaves, residue of water plants and fish waste pollute the pond. The Bio-Oxydator from Velda ensures that all waste is broken down. This product effectively removes pond sludge and adds oxygen to the water.