Summer is the warmest and sunniest time of the year. The warm water temperatures boost you Koi's metabolism and their immune system. Summer is the grow out period for Koi, they'll easily eat 3-5 times a day. You just have to make sure that your filter can handle all of your Koi's waste, otherwise they will suffer from a buildup of ammonia and dissolved solids in the water. Also, if you don't have a sufficient size filter, your pond will probably end up looking like a bowl of split pea soup!
One thing that you have to watch in the summer is your DO (dissolved Oxygen) level. The warmer your water, the less oxygen it can hold. Keep an adequate amount of aeration going in your pond at all times. It doesn't matter if it is an air pump and air stone, or a large waterfall. The minimum level that Koi need is 4 ppm (parts per million). Keep in mind that 4 ppm is the minimum level, the DO level should always be well above that. Your Koi need oxygen to live.
The ideal temperature for Koi in the summer is around 70°F - 75°F. This is the most comfortable temperature range for them. Watch out for those dog days. If you have a shallow pond, the water temperature could rise up to dangerous levels and your Koi could suffer. Provide some cover or some shade for your Koi, so they have a place to get out of the direct sunlight.
Koi love to eat bugs. It is not uncommon to hear them splashing around at the surface at night while they try to get insects that are near the water's surface. Eating bugs, along with their daily feedings and warm water temperatures, will make them grow very fast.
Back to Koi Care.