The number one thing you must do is keep the water clean and keep testing it. You need to test the pH, hardiness, ammonia, nitrates, and nitrite levels. This testing is important to keeping your fish alive.
There is three different types of pond filters. These are mechanical, chemical, and biological. The biological comes in up flow, down flow, and lateral flow. Adding a skimmer is something to think about. This helps you clean debris off the top of the pond.
Aeration is also important for oxygen for your fish. Some examples of aeration would be a waterfall or a fountain. Pumps can be added if you don’t want these features.
One of the hardest things to beat is algae. Algae can take over your pond. Especially if it is in the direct sunlight. It can also be caused by high nitrate levels. Try adding a UV sterilizer and doing a partial water change.
New ponds take time before fish can be added. Test the water regularly and hopefully within 4-6 weeks you can add your fish. You can be adding your new plants while you are waiting.
A bottom drain for you pond is really handy. If you didn’t add one you may want to consider adding one. Also and overflow pipe comes in handy when it rains or snows.
Cleaning the pond is critical. You need to remove leaves from the top and vacuum the dirt that collects on the bottom. If you have a bottom drain you can open it to remove dirt too.
Winter time means that you need to keep the pond from totally freezing over. You may have to shut down your filter, but you can buy a pump to help keep water circulating. The pond can also be covered to protect it from debris.
Spring is a time for cleaning. Summer is when you need to monitor algae growth and do partial water changes. Fall is when you need to watch for falling debris. Remove any debris and dying plants in your pond.