External vs. Submersible Pond Filters

There is a vast array of available pond filters. Each with its advantages and disadvantages.  Submersible filters  sit inside the pond. Often installed with a fountain pump, they are capable of providing mechanical and biological filtration to smaller ponds. External filters come in a wide variety of shapes and sizes. They can be any size, and will sit outside of the water garden or koi pond, with water piped from the pond and back into it. Although more complicated, external filters provide much greater flexibility when it comes to filtration systems.

Submersible Filters are a simple way to add filtration to small ponds. They are self-contained and  often return water through decorative fountains, making them a pleasing addition to the pond. The drawbacks of submersible filters are generally maintenance related. To perform routine maintenance, the filter must be retrieved from the bottom of the pond, making this an impractical option for larger ponds and can be difficult for seniors to manage long term. They also lack the flexibility of external models; however, a few models incorporate ultraviolet clarifiers making them excellent all-in-one solutions for smaller ponds.

External filters are the overall more effective of the two styles in mid-size and larger ponds. Usually they can be easily hidden from view, maintaining the natural look most pond owners enjoy. The can be easily accessed for routine maintenance, making it less of a hassle, and as such, more likely to performed on a regular basis. They are very flexible, with a variety of components that can easily be incorporated into their design, including UV, bio-media, filter mats and pads  They can also be as expensive or inexpensive as the pond owner can afford.  With effective models at every price point.  The main drawback to external filtration can be their size and difficulty to add to a small system. They must be connected to a separate external or submersible pump.    

Both submersible and external filters have a place in pond gardening. Submersible filters work very well for smaller ponds. They are great for beginners, as they are easy to assemble and work with. They can a valuable addition even to larger ponds with external filters, as they can be used for their decorative fountain attachments and as additional mechanical or chemical filtration. External filters should be the standard system for all but the smallest of ponds. They are very functional, flexible, and will provide the best functionality of the two. They can easily be plumbed into waterfalls and streams, and be hidden from view. If used in conjunction with an overflow device, external filters can provide a unique, natural environment that a submersible filter simply cannot.

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