While it might not seem like it at first glance, just about everything that happens in your pond, good and bad, comes down to metabolism. The health and cleanliness of your water is an interplay between the metabolisms of algae, bacteria, plants, and fish. Sunlight, rain, oxygen levels, bacteria and algae ratios, temperature, organic waste, and about a thousand other things can affect the metabolisms of the life in your pond in ways subtle and obvious. A lot of these factors are difficult or impossible to control or predict, and all we can do is enjoy the results or deal with the fallout of these processes.
Some things about how metabolism affects your pond, though, are fairly easy to predict and control. One of the best examples is how water temperature affects the metabolisms of fish. Pond fish are cold-blooded, so their metabolisms are heavily affected by weather. As the water around them gets colder, their metabolisms slow more and more. Fortunately, we can deal with this slowdown fairly easily by changing what and how often we feed them.
The simple rule is this: when the water temperature is below 55 degrees F, switch from normal food to cold-water fish food. When it drops below 42 degrees F, stop feeding them entirely.
The reason we stop feeding them below 42 degrees is fairly simple: at that point, your fish’s metabolism has slowed enough that they’ll hardly need to eat at all, so any food you give them will simply be rotting in the water and negatively affecting your water health. This is complicated by the fact that algae and bacteria metabolisms are slowed, too, so the extra organic material won’t be dealt with effectively by the rest of your pond ecosystem.
Above 42 degrees, though, it’s much more complicated (though not harder to deal with). Your fish still need to eat between 42 and 55. Their metabolisms are slower, though, and that has made their digestive tract much less effective. Cold water fish food has been designed by people who are much smarter than I am to be easy to digest and to only give your fish what they need for this slower metabolic state.
The consequences of continuing your normal feeding routine below 55 degrees can be quite serious for your pond. The incompletely digested or uneaten food that your fish leave in the water can’t be dealt with by your pond bacteria at this temperature, and that can leave your fish spending the entire winter in badly out of balance water, add significantly to the unhealthy sludge layer of your pond, and cause massive spring algae blooms. Worse, the slowed digestion of the overly-rich food can cause serious direct health problems for your fish, and can even cause what can only be described as fatal constipation. This is why I strongly recommend a switch to cold water fish food at lower temperatures. It’s a very easy solution to what can be a big problem for your pond.