After setting up your pond with a pump and filter, make sure to add Fresh Start when you fill the pool. With the filter running (you can run your fountain or waterfall at this stage), leave it all to settle for at least 24 hours to ensure everything is working correctly and allow the water temperature to stabilise.
Only introduce one or two fish at the start. The trick is to increase fish quantity slowly over a period of three months to allow the life support system to mature. After three months, by which time the life support system will be mature, fish feeding can be gradually increased, and the frequency of the partial water changes reduced. You will now have a healthy, matured pool.
Careful attention in these early weeks will pay for itself in an easy to maintain, and healthy home for your fish.