Thank you so much for this advice. It’s important to clean a garden pond in a way that is safe for plants and fish. The easiest way to keep it clean is to install a filter and pump. You’ll only need to change the filter medium once in a while. Just be sure there is an intake screen to protect fish. Without a filter system, cleaning the pond by hand once a year should be adequate. Remove debris by hand or with a net. If the water is still pretty dirty, drain the pond and give it a good scrubbing. You’ll have to move any fish and plants briefly to do this. Keep fish in water and plants moist. Read here about pond filter - https://www.backyardstyle.com/best-pond-filter.