TetraPond CrystalWater 250ml works to clear dirty pond water by binding dirt particles together, causing them to sink to the bottom of the pond to be cleared by hand or by a water filter. Harmless to pond environments and fish, murkiness will quickly be replaced by clear water so that you can enjoy your pond fully. The product works in a matter of hours and is an efficient way to help clear fish waste, dead plant material and uneaten food, improving the health of fish and other pond inhabitants.