Hello Maya ! I think in a pond the best thing is a bubbler of course or a pump to recirculate and aerate the pond bringing oxygen to the water! But I would imagine most people know that! Also a good combination of fish, top feeders bottom feeders and inbetween feeders! I have a small pond about 8ft diameter about two and a half foot depth with a little bay about a foot deep! With an over hanging Chinese maples and other assorted plant life surrounded by indigenous sandstone! If algae gets too thick I scope it out with a bucket and use the water in the garden and refill it with fresh well water! It has created a little ecosystem of life with tree frogs toads and tadpoles,birds, ground squirrels, garden snakes and cats and dogs love the water ,preferring it to fresh clean looking tap water! I havent imported fish to the pond recently but it still has a life of its own! Its wonderful and children just adore it, big children too!