Koi keeping is an important part of Pond Care and stress is an impending part of it. We all go through stress in our lives to being uncomfortable and new to something. Fish living out in nature would simply swim away from stressful conditions, but when they are confined in a pond or tank there is no way for them to swim away. Ammonia levels can get too high and this can cause them a lot of stress. Fish have a hard time dealing with change in their environment, including temperature. That is why when you move any fish from one water source to another they need to be acclimated before being put in. This goes for pH, hardness and alkalinity of its new home.