With these elements present, with the exception of some seasonal maintenance, all you need to do is add beneficial bacteria and clean out the skimmer net every other week. In our altitude in Colorado Springs you may also need to add a product to help keep the string algae under control. Mechanical filters or skimmers act like a pool skimmer and filters out large items such as leaves and twigs from the pond. You should clean this out as needed. Usually once or twice during the summer and more often in the fall when vegetation looses leaves. If you have a large wind storm, check the skimmer to see if there is additional debris that needs to be removed. A Biological filter is the filter that catch and grow the beneficial bacteria colonies so that when water passes thru these colonies, the bacteria cleans the water. Do not clean these filters more than once a year or you will kill off the bacteria colonies. It is a must to have the proper pump for your feature. It is good to have a pump that circulates your water through the filters one time each hour. Rocks and gravel protect the liner so that it will last longer in the sun. They also provide additional surface area for bacterial colonies to grow on. Plants and fish keep the ecosystem balanced with their roots and waste.