Cleaning water is done through the biological filtration system and UV light. If you don't have a biological filtration system then you can clean water using water treatments from the Oase and Clearpond range. A pump is still needed to circulate the water treatment throughout the pond.
Don't use chlorine in ponds or water features because it will kill your fish and plants, stain your walls or water feature and damage the pump voiding its warranty.
There are a large amount of filtration and water treatment products that are safe for your pond life and equipment, please browse through the filtration and water treatment sections for more information.