Pond Fish Kill

Most pond fish kills are a result of insufficient oxygen levels in the body of water.  Insufficient oxygen levels can be caused by several different situations.  The first is decomposition of vegetation and the second is water temperature.

            Ponds that experience an excess amount of nitrogen and phosphorous from lawn and pasture fertilizer run off to septic leakage are going to be very susceptible to an increased amount of weeds and algae and pond fish kill.  Some vegetation is beneficial for a pond.  Fish will have a place to spawn, have a food source, and the weeds can help with oxygen levels.  Pond bacteria products can help reduce and maintain the amount of excess nitrogen and phosphorous minimizing your algae and weed growth. 

            However, weeds and algae can quickly take over a pond.  Aquatic approved herbicides and copper products like our Tsunami DQ and Crystal Plex can be used to help control weeds and algae.  Aquatic herbicides like the Weed Plex Pro are safe for use in fish ponds when used according to directions.  It is recommended that you treat only a section of the pond at a time to prevent total oxygen depletion.  If the entire pond is treated at the same time all of the decomposing material will create an oxygen deficit and a pond fish kill.  Copper products are also safe for most fish.  Some species such as Koi and Trout are extremely sensitive to copper and will die.  Almost all pond fish kills that occur after a copper treatment are the result of a major algae kill, which depletes the oxygen not the copper itself.

            The other cause of oxygen depletion is the water temperatures.  In the middle of the summer during the hottest month’s water temperatures can increase drastically.  Warmer water holds less oxygen in general and the smallest treatment for weeds or algae in the summer can cause a pond fish kill.  Aeration systems can help circulate cooler water at the bottom of the pond to the top to keep pond water temperatures balanced.    

            The solution is to be cautious when treating for weeds and algae.  Follow all label instructions, treat in spring and fall so high risk mid-summer treatments can be reduced, treat only a portion of the pond at a time, install an aeration system, and monitor your fish activity a week after treatment.  If you are proactive and a bit knowledgeable you can prevent pond fish kill.