Article - What About the Heat?
Summer Heat and Ponds
How does the heat affect your koi, you say? Well, koi are temperate zone fish, not tropical fish. So they are not as suited to hot conditions as you might think. They are suited to temperatures between 39 and 85 degrees Fahrenheit. Under 39F, they may not survive. Over 85F, they will also suffer, may not process food well, and their systems will slow down. This is the reason we don’t recommend feeding as often in the very high temperatures of summer. This is particularly troublesome in shallow ponds in the warmer Southern zones.
And they can become sun burned if they have no shade. Shade is very important for koi and can be provided by erecting a pergola or planting shade trees near the pond, preferably on the west side of the pond as the heat is most severe later in the day. If the filters are shaded, or the waterfall, the water will be cooled by circulating through them and back into the pond. You may notice your koi staying near the bottom in the heat of the day. There are “tunnels” that can accomplish shade for the fish and are fish-safe to put in the bottom of the pond, but they will restrict the water flow to a bottom drain.
The best way to protect your koi from summer and winter weather extremes is to dig the pond as deep as possible. In the same way ice floats in a glass of water, the coldest water will float to the top of the pond in winter. And in summer, the hottest water will be on the top of the pond. It is called thermal inversion. So the most stable temperatures will be on the bottom of the pond if the pond is deep enough to provide comfortable temperatures. Just take a run down to the cellar and see how much better it is down there and you will see what you need to do for your fish. By digging deeper rather than wide, you will be doing a very big favor to your fish!