Why does pond water temperature matter?

koi pond backyard water feature

Why does pond water temperature matter?


As the pond water temperature gets colder, the lowest levels of the pond are deeper in the earth and are actually warmer.  That is why the fish stay there for the winter.  When we add in aerators the frigid air pumped to the lowest water in the pond can disturb the temperatures.  Place aerators in an upper level in the pond.  If your pond doesn’t have built-in shelves, put a bucket or pot upside down and place the aerator on top of it to raise it up from the lowest level.

Feeding the fish

When the water temperatures reach 50° we need to stop feeding the fish.  Their metabolisms slow down at 50° and they are unable to digest food.  When they eat, it will sit in their digestive tract and rot if they cannot process it.  They may be found dead midwinter or even in the spring if they are fed past the point that they can process it.


Regular bacteria does not thrive when the water is 50° in the pond.  Use coldwater bacteria until the water gets down to 45°.  Then after that, stop adding bacteria until the spring when the water warms up!


Plants need to be cut back for the winter.  It is best to cut lilies and lotus back AFTER the leaves have turned brown.  Cut them to 4 -6 inches above the root ball.  Marginal plants (plants whose roots are in the water) should be cut back once they start to turn brown to about 4 inches above the root ball.  Putting your lilies at the lowest point in the pond for the winter helps keep them healthy because the water is warmest at the bottom of the pond during the winter.

Keeping leaves out

When the water temperature gets down to 50° you better believe the leaves are about to start falling.  Trim back plants that hang over the pond so they don’t drop in dead foliage.  To keep organic material out of your pond, put a net on it!


Remove Autodoses, IonGens and UV lights from the pond for the winter when the water gets down to 50°.