Evolution Aqua Pure Pond are biodegradable balls which contain live bacteria which is slowly released into your pond when they are needed most. With over 8,000,000,000 bacteria per litre of Pure Pond Balls, your pond will shine even more than normal. They make even more of a difference if you add them monthly into any type of filter. 500ml treats ponds up to 10,000 litres. 1000ml treats ponds up to 20,000 litres. 2000ml treats ponds up to 40,000 litres. Bomb treats ponds up to 20,000 litres