Submersible Pond Filters vs. External Pond Filters: Gravity Flow and Pressurized
Author: Terry Newhaven
Like a swimming pool requires chlorine and other chemicals to keep it clean and swimmable, ponds need filtration systems in place to keep the water clear and sustainable for the life in and around it. If you have fish in your pond, filtration is definitely needed to clear the pond of their waste and help support a natural nitrogen cycle. There are several filters to choose from, each varying in price and level of efficiency.
Submersible filters are great for beginning small pond owners because of their incredibly simple setup. Designed to be unobtrusive, they tend to contain a built in pump, spray attachments and are self-contained. The spray attachments are used to return the water back to the pond once it passes through the filter. The attachment can also be used to hide the filter box and it's cords. They're better for small ponds because the filter has to actually be removed from the pond in order to do any kind of maintenance on it. They are energy efficient as well. Some submersible filters now incorporate UV sterilizers into the filter.
External filters are better for larger ponds or ponds that have a lot of fish. Maintenance is simple because they are located outside of the pond. Most models have a strainer basket that can be removed to empty debris that is filtered from the pond. External filters are also easily expandable, allowing other components to be incorporated into the system, like UV filters. Users can make an external filter from inexpensive parts or can purchase one from a pond supply store. External pond filters available for purchase will usually fall into two categories: Gravity flow and Pressurized.
Gravity flow filters are external filters that utilize a pump to push cleansed water into the pond at the same rate that water is being filtered out of it. Because they aren't pressurized, these filters need to be physically placed above the pond they are flowing into, utilizing gravity to filter the pond. Users can also use biological filtration and UV clarification in addition to gravity flow filters to guarantee clear and purified water.
Pressurized filters are external and can be used when water that has already been filtered needs to be pumped to an elevated area, like if the pond has a waterfall. Many pressurized filters come in a variety of sizes and are very efficient. One advantage pressurized filters have over gravity flow filters is that pressurized filter locations aren't limited to being above the pond. They require a pump with a higher water flow than gravity flow filtration systems do to account for the additional distance and height of where the water will eventually be returned to the pond.