You may look at your pond in winter and wonder what the water temperatures are. If there is ice floating on the surface, the temperatures will be around freezing point there. But what about deeper down? Water has a special property, different from many other liquids (anomaly of water): it has its highest density at 4 °C and expands when it cools down. This is why ice floats on top of water. Pond owners often use a pond thermometer to find out what the water temperatures in their pond are. However, they should remember that most thermometers, like the JBL Termómetro estanque , float on the surface and only show the water temperature there. At a depth of one metre, the temperature will (hopefully) be higher - usually around 4 °C in winter. This is where the fish rest, winding down their metabolisms.
To find out the temperatures in your pond water at different depths, tie a knot every 50 cm in the cord starting from the thermometer, put a weight on the thermometer and lower it. Wait a few minutes until it has taken on the ambient temperature of the respective depth and pull it up quickly. This is the quickest way to find out whether everything is as it should be in your pond! If the water temperature is lower than 4 °C even in its deep parts, the "warm" deep water will probably be circulating elsewhere and your pond will freeze through. This endangers not only your fish, but also the microorganisms! Therefore, never aerate or siphon off water (for filters or watercourses) at the deepest point of the pond.
Always position pumps and air stones so that they are at least 50 cm above the ground. This way your pond and its inhabitants will survive the winter without any problems! With the new automatic pond feeder, the JBL PROPOND AUTOFOOD , a temperature sensor with a three-metre cable is included for these reasons, and the display shows the water temperature realistically.