Some parts need replacing in the spring so you can enjoy a perfectly clear pond.
The oxygen content in the pond water is very important for life in the pond. The solution to oxygen problems is always a strong air pump that gets the deeper water layers moving properly.
You spend a lot of leisure time on your pond and your fish. It's fair to say that your pond is your hobby. So it's frustrating to see your precious fish disappear one by one. Cats and especially herons like to eat up the fish in your pond.