The pH should not rise much above 8.5 at its maximum reading. Koi have adapted to survive in a pH range of 6.5 - 9. Providing the fluctuation within this pH range in not large and providing the pH change is not sudden. On most occasions temperature will be lowest in the morning just before sunrise and the highest at sunset. Temperature is influenced by the amount of sun, the intensity of the sun the pond receives and other factors such as the wind speed during the day or night.
Evaporation cools the water.
Generally speaking koi should not be subject to more than a 3 - 5 C sudden change in water temperature. Always adjust the temperature gradually when moving koi around. An upward movement is tolerated better than a downward movement in temperature. Koi are more affected by temperature variations at lower water temperatures. And you will notice koi are more affected by a sudden lowering of water temperature than a sudden raising of water temperature.