There are various forms of algae that grow in a water garden, and when kept under control, some algae is desirable because it acts as a water purifier and a home to necessary microorganisms. A well-balanced water garden has a thin layer of algae on everything that is under water.
Many gardeners use a combination, such as creating a natural balance aided by filters and bacteria.
A natural balance is created by installing water garden plants, scavengers, and ornamental fish in proper quantities. Plants with floating leaves, such as lotus and water lilies, are most important because they reduce the penetration of sunlight into the pond, keeping the water at a cooler, more constant temperature. Try to cover 50 to 75 percent of your water garden surface with plants with floating leaves. Scavengers, such as snails, mussels, and tadpoles, are essential because they consume organic wastes that settle to the bottom of the pond, they graze on the sides and surfaces of the pond, and they consume suspended algae in the water. Most people choose to add fish, such as goldfish and koi, for their ornamental and aesthetic value.